[fortran, patch] Fix display of locus when source contains wide characters

[FX]

The attached patch fixes PR 36160 
(http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36160). It should correctly 
account for wide characters when display error loci. I'm not sure if we can 
check that in the testsuite harness, but you can manually see it at work on the 
attached test.f90.

Bootstrapped and regtested on x86_64-apple-darwin11, OK for trunk?
FX

widechar_locus.ChangeLog
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widechar_locus.diff
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test.f90
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