Refactor includes.
* gettext-tools/src/read-catalog-abstract.h: Include <stdio.h>. Don't include
po-lex.h.
* gettext-tools/src/read-catalog.c: Include po-lex.h.
* gettext-tools/src/msgcmp.c: Include po-lex.h.
* gettext-tools/src/msgfmt.c: Likewise.
* gettext-tools/src/msgmerge.c: Likewise.
* gettext-tools/src/xgettext.c: Likewise.
* gettext-tools/libgettextpo/gettext-po.c: Likewise.
* gettext-tools/src/x-po.c: Include <error.h>. Don't include po-lex.h.
* gettext-tools/src/read-desktop.h: Include pos.h. Don't include po-lex.h.
* gettext-tools/src/read-desktop.c: Don't include po-lex.h.
