Use full name for m4/gnulib-comp.m4. (Bug#11529)

Use full name for m4/gnulib-comp.m4.  (Bug#11529)

Previously the file was named m4/gl-comp.m4 due to DOS 8+3 restrictions,
even though the file's name in gnulib is m4/gnulib-comp.m4.
This had a problem when merging from gnulib, as the code temporarily
renamed it to the full name, causing problems when interrupted.
Now the file has its full name, with the idea that we will find
a solution for MS-DOS that does not affect the rest of Emacs.
* m4/gnulib-comp.m4: Rename from m4/gl-comp.m4.
* admin/merge-gnulib: Leave m4/gnulib-comp.m4's name alone.