Bug 1038570 - Part 1: rename nsObjectFrame.* to nsPluginFrame.*, changes moz.build and includes. r=dbaron

--HG--
rename : layout/generic/nsObjectFrame.cpp => layout/generic/nsPluginFrame.cpp
rename : layout/generic/nsObjectFrame.h => layout/generic/nsPluginFrame.h
Bug 1038570 - Part 2: rename ObjectFrame class to PluginFrame. r=dbaron
Bug 1038570 - Part 3: rename ObjectFrame variables to PluginFrame. r=dbaron