More renaming from 'getdate' to 'get_date'. * doc/get_date.texi: Renamed from doc/getdate.texi. * modules/get_date (Files): Update. * MODULES.html.sh (Date and time <time.h>): Update. * DEPENDENCIES: Update. * gnulib-tool: Update comment. * m4/bison.m4 (gl_BISON): Likewise. * m4/get_date.m4 (gl_GET_DATE): Likewise.