Remove some trailing spaces in source.c

gdb/ChangeLog:

        * source.c (substitute_path_rule_matches): Remove trailing spaces.
simplify substitute_path_rule_matches using filename_ncmp

At the time this function was written, there was no filename_ncmp,
only FILENAME_CMP. So, in order to do an n-cmp, we had to make a local
copy of the first n characters of our string and use that to perform
the comparison. This patch simplifies the function's implementation,
now that we have filename_ncmp.

gdb/ChangeLog:

        * source.c (substitute_path_rule_matches): Simplify using
        filename_ncmp instead of FILENAME_CMP.

Tested on x86_64-linux.
Unnecessary restore of timeout global at end of gdb.base/completion.exp

This patch removes some code in gdb.base/compilation.exp which
is aimed at restoring the original timeout global value after having
changed it for this testcase. Restoring the timeout global is not
necessary as this is taken care of by gdb_init, which is called
at the start of each testing.

gdb/testsuite/ChangeLog:

        * gdb.base/completion.exp: Remove code aimed at restoring TIMEOUT.