Fix of failure in_of_string on Windows.
Fix of failure in_of_string on Windows.

The file of the form "file:line:col1:col2" was created, than split on ":"
and and int_of_string was used to get line number and colon numbers. This
failed on windows because the file name contained ':', i.e.,
"C:\...\gnatprove\p\..\p.mlw:2254:55:150".

ssaavedra/why3,ssaavedra/why3,ssaavedra/why3