Improvements to exp_guild.txt loading

- Modified exp_guild.txt processing to honor the value of MAX_GUILDLEVEL
  and correctly handle overflows.

Signed-off-by: Haru <haru@dotalux.com>
Improved questlog handling to honor the value of MAX_QUEST_OBJECTIVES

Signed-off-by: Haru <haru@dotalux.com>
Renamed atcommand->parse to atcommand->exec

- Renamed function to a more appropriate name.
- Changed its last argument 'int type' to 'bool player_invoked' to make
  its purpose more obvious.

Signed-off-by: Haru <haru@dotalux.com>
Minor fixes to the strlib interface

- Fixed a typo in the strnlen() macro (was strnln)
- Initialized strlib->strnlen and strlib->strtoull to NULL on platforms
  that don't require them. Please note that those two functions are
  supposed to never be called directly but only through the strnlen()
  and strtoull() macros, which take care of the platform abstraction.
- Removed localized versions of yes/no from config_switch (if you really
  want to be able to use "oui", "ja", "si", "non", "nein", feel free to
  add them back yourself following the example in strlib.c)

Signed-off-by: Haru <haru@dotalux.com>
Compatibility fixes for NetBSD and Solaris

- Fixed some warnings in NetBSD (5.x and 6.x) and Solaris (11)

Signed-off-by: Haru <haru@dotalux.com>