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.

docs/devinfo.html

@@ -107,7 +107,7 @@ Global variables are not allowed.
 Function name examples:
 </p>
 <pre>
-	glFooBar()       - a public GL entry point (in dispatch.c)
+	glFooBar()       - a public GL entry point (in glapi_dispatch.c)
 	_mesa_FooBar()   - the internal immediate mode function
 	save_FooBar()    - retained mode (display list) function in dlist.c
 	foo_bar()        - a static (private) function

docs/dispatch.html

@@ -244,8 +244,8 @@ isn't a significant problem.</p>
 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>