Fix bug #11959 with startup warnings on MS-Windows about ../site-lisp.

src/w32.c (init_environment): Change the default values of many
 environment variables in dflt_envvars[] to NULL, to avoid pushing
 them into environment when they were not already defined.  Remove
 the code that deletes site-lisp subdirectories from the default
 value of EMACSLOADPATH, as it is no longer needed.
 (check_windows_init_file): Now external, not static.  Use
 Vload_path as is, without adding anything, as this function is now
 called when Vload_path is already set up.
 src/w32.h (check_windows_init_file): Add prototype.
 src/emacs.c (init_cmdargs) [WINDOWSNT]: When running from the build
 directory, ignore the /*/i386/ tail in Vinvocation_directory, for
 compatibility with Posix platforms.
 (main): Move the call to check_windows_init_file to here from
 w32.c.
 (decode_env_path) [WINDOWSNT]: Expand the %emacs_dir%/ prefix, if
 any, in the DEFALT argument into the root of the Emacs build or
 installation tree, as appropriate.
 src/callproc.c (init_callproc_1): Call decode_env_path instead of
 doing its equivalent by hand.
 (init_callproc): Replace DOS_NT condition with MSDOS, thus letting
 the code that sets Vexec_path run on MS-Windows.
 src/lread.c (init_lread): Add comments to #ifdef's.

 nt/paths.h (PATH_LOADSEARCH, PATH_SITELOADSEARCH, PATH_EXEC)
 (PATH_DATA, PATH_DOC): Replace dummy directory names with
 directories relative to %emacs_dir%.
 (PATH_EXEC): Add lib-src/oo-spd/i386 and lib-src/oo/i386, to cater
 to the use case of running un-installed Emacs.

nt/paths.h

@@ -18,14 +18,18 @@ GNU General Public License for more details.
 You should have received a copy of the GNU General Public License
 along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
 
+/* Relative file names in this file that begin with "%emacs_dir%/" are
+   treated specially by decode_env_path: they are expanded relative to
+   the value of the emacs_dir environment variable, which points to
+   the root of the Emacs tree.  */
 
 /* The default search path for Lisp function "load".
    Together with PATH_SITELOADSEARCH, this sets load-path.  */
 /* #define PATH_LOADSEARCH "/usr/local/lib/emacs/lisp" */
-#define PATH_LOADSEARCH "C:/emacs/lisp"
+#define PATH_LOADSEARCH "%emacs_dir%/lisp;%emacs_dir%/leim"
 
 /* Like PATH_LOADSEARCH, but contains the non-standard pieces.  */
-#define PATH_SITELOADSEARCH "C:/emacs/site-lisp"
+#define PATH_SITELOADSEARCH "%emacs_dir%/site-lisp;%emacs_dir%/../site-lisp"
 
 /* Like PATH_LOADSEARCH, but used only when Emacs is dumping.  This
    path is usually identical to PATH_LOADSEARCH except that the entry
@@ -39,13 +43,13 @@ along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
    variable exec-directory.  exec-directory is used for finding
    executables and other architecture-dependent files.  */
 /* #define PATH_EXEC "/usr/local/lib/emacs/etc" */
-#define PATH_EXEC "C:/emacs/bin"
+#define PATH_EXEC "%emacs_dir%/bin;%emacs_dir%/lib-src/oo-spd/i386;%emacs_dir%/lib-src/oo/i386"
 
 /* Where Emacs should look for its architecture-independent data
    files, like the NEWS file.  The lisp variable data-directory
    is set to this value.  */
 /* #define PATH_DATA "/usr/local/lib/emacs/data" */
-#define PATH_DATA "C:/emacs/data"
+#define PATH_DATA "%emacs_dir%/etc"
 
 /* Where Emacs should look for X bitmap files.
    The lisp variable x-bitmap-file-path is set based on this value.  */
@@ -53,11 +57,10 @@ along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
 
 /* Where Emacs should look for its docstring file.  The lisp variable
    doc-directory is set to this value.  */
-#define PATH_DOC "C:/emacs/etc"
+#define PATH_DOC "%emacs_dir%/etc"
 
 /* Where the configuration process believes the info tree lives.  The
    lisp variable configure-info-directory gets its value from this
    macro, and is then used to set the Info-default-directory-list.  */
 /* #define PATH_INFO "/usr/local/info" */
 #define PATH_INFO "C:/emacs/info"
-