Bug 999881, part 1: Replace charsetOverlay.xul in the message reader, r=mconley.

--HG--
rename : suite/common/charsetOverlay.xul => mail/base/content/charsetOverlay.xul
extra : rebase_source : 8e858435e679734d2bcc77100a852cfab77f5ac1
Bug 999881, part 2: Replace charsetOverlay.xul in the compose window, r=mconley, a=jcranmer.

--HG--
extra : rebase_source : 1145a0b70cc552b8228dc47859ef9d4d71c64871
extra : amend_source : e4cef33f4c44f5661e322e517f925534023b9e8b