Fix ggtags-find-project to check on the GTAGS file

Note: this is to reduce false positives in case-insensitive file
systems.

Improve ggtags-include-pattern to strip leading ../ in path.
New macro ignore-errors-unless-debug and use it
Cosmetic change: Fix indentation
New helper ggtags-forward-to-line and use it

Simplify ggtags-list-of-string-p with cl-every.
New feature ggtags-global-restore-search for #37
Polish last change

- Replace 'restore' with 'rerun' which seems clearer.
- Remember last position in ggtags-global-rerun-search and kill the
  search buffer on quit or done.
- Make sure ggtags-global-search-history is ordered by access time.
Also record ggtags-process-environment in search history
Bind ggtags-save-to-register in ggtags-global-rerun-search-map
Disable ggtags-navigation-mode in ggtags-global-rerun-search
Support search bookmarks as requested in #39

New variable ggtags-global-history-length.
Fix #40: New user variable ggtags-supress-navigation-keys