maint: change "time stamp" to "timestamp" globally

maint: change "time stamp" to "timestamp" globally

This avoids a new syntax-check failure.
* ChangeLog-2007: Perform that change.
* NEWS: Likewise.
* algorithm.doc: Likewise.
* doc/gzip.texi: Likewise.
* gunzip.in: Likewise.
* gzip.1: Likewise.
* gzip.c: Likewise.
* gzip.h: Likewise.
* m4/.gitignore: Likewise.
* sample/ztouch: Likewise.
* tests/timestamp: Likewise.
* unzip.c: Likewise.
* zip.c: Likewise.
* znew.1: Likewise.
* cfg.mk: Update the old news hash accordingly.