Mostly a cleanup of gutils/gimagereadras.c ....

Mostly a cleanup related to gutils/gimagereadras.c, such as converting gallocs to mallocs, lots of file checks for bad reads. Found issue with FF not recognizing *.ras, so also had to patch gimageread.c to use the summer2012 filename.suffix as a backup in case gtk/giomime doesn't have an answer (maybe the list isn't complete).