fixed Cygwin+MSVC build errors. The ICC profile handling now includes more
checking.  Several errors that caused rejection of the profile are now
handled with a warning in such a way that the invalid profiles will be
read by default in release (but not pre-RC) builds but will not be
written by default.  The easy part of handling a cHRM chunk is written,
where the ICC profile contains the required data.  The more difficult
part plus guessing a gAMA value requires code to pass selected RGB values
through the profile.