Add experimental RGUI keyboard search feature.

Type '/' to start search, then type search string (case sensitive for
now due to strcasestr being GNU ext). When done, type return.
Merge branch 'master' into rgui-search
Refactor keyboard event callbacks.

Go through input/keyboard_line.c to better hide internal logic
regarding keyboard line input.
Update griffin.
Fix CXX_BUILD.
Fix menu_search_callback.

str can be empty and non-NULL.
Use strcasestr.

Since it's a GNU extension, move to strcasestr.h.
Add strcasestr check to quickbuild.
Prioritize matches with first chars.
(iOS) Split some code from menu.m info functions for re-use.
(OSX) Fix support for gamepads that aren’t a WiiMote or DualShock 3.
(OSX) Fix frontend/frontend.c so passed arguments are accepted.
(Apple) Fix mapping of gamepad negative axis; the input binding menu now polls the proper gamepad rather than always polling player 1’s.
Merge pull request #410 from libretro/rgui-search

Add experimental RGUI keyboard search feature.
(OSX) Consolidate mouse handling into NSApplication’s sendEvent method. Cleaner overall and fixes issue where relative movement was unavailable from track pads.
(OSX) Properly process modifier keys
(iOS) Fix potential crash in structure returned by apple_get_frontend_settings.
(iOS 7) Bring back keyboard mode
Add SSE3 detection to performance.c (check if this is correct)
Merge remote-tracking branch 'upstream/master'

Conflicts:
	qb/config.libs.sh