maint: correct misuse of "a" and "an" * doc/regex.texi (Collating Symbol Operators): s/an close.../a close/ * lib/argp-help.c: "an docum...": s/an/a/ * lib/argp-parse.c: "An vector": s/An/A/ * lib/execute.c: "an native": s/an/a/ * lib/spawn-pipe.c: Likewise. * lib/gc.h: "an Gc_rc": s/an/a/ * lib/unigbrk.in.h: "an grapheme": s/an/a/ * lib/fts.c: "an stat.st_dev": s/an/a/