glapi: Move src/mesa/main/dispatch.c to glapi and rename.

main/dispatch.c is a glapi source file.  It is part of GLAPI_SOURCES in
sources.mak and part of glapi_sources in SConscript.  This commit moves
it to glapi/ and renames it to glapi_dispatch.c.
diff --git a/docs/dispatch.html b/docs/dispatch.html
index bcab74c..0c54a84 100644
--- a/docs/dispatch.html
+++ b/docs/dispatch.html
@@ -244,8 +244,8 @@
 system.  There are two steps to this.  The file must first be added to
 <tt>src/mesa/sources</tt>.  That gets the file built and linked.  The second
 step is to add the correct <tt>#ifdef</tt> magic to
-<tt>src/mesa/main/dispatch.c</tt> to prevent the C version of the dispatch
-functions from being built.</p>
+<tt>src/mesa/glapi/glapi_dispatch.c</tt> to prevent the C version of the
+dispatch functions from being built.</p>
 
 <A NAME="fixedsize"/>
 <H3>3.4. Fixed-Length Dispatch Stubs</H3>