changed makefile-mac to build Golly using wx3.x, and to link the right Perl lib if running on 10.6 or 10.9
removed .bmp files from bitmaps folder (wxMSW now uses .xpm files)
added XPM_BITMAP macro to avoid segfault in wxGTK app
fixed button sizes in Mac app when building with wx 3.x
fixed missing gap between layer bar buttons in Mac app when building with wx 3.x
use nicer looking toggle buttons in Mac app's layer bar when building with wx 3.x
updated version to 2.7b2
fixed some spacing problems in Mac app's Prefs dialog when building with wx 3.x
fixed problem using return key to select OK button in some dialogs when building Mac app with wx 3.x