MosaicMainWindow.h: 2012-03-13 Steven Lambright - m_lastOpenedFile wasn't...

MosaicMainWindow.h: 2012-03-13 Steven Lambright - m_lastOpenedFile wasn't being initialized or set properly causing the file open dialogs to always open to '/' which was undesired behavior. This has been fixed by initializing it to '.' and updating its value  when a cube is opened. Fixes #752. 

git-svn-id: http://subversion.wr.usgs.gov/repos/prog/isis3/trunk@4114 41f8697f-d340-4b68-9986-7bafba869bb8