OSX: Improve error handling for defective/corrupt/troublesome fonts.

If font enumeration has trouble enumerating one or more fonts, only
print the problem description at verbosity level >=3 or on critical
failure (when no font could be enumerated at all). Also printout the
troubleshooting hints only once per error and tell user how to shut it
up.

Additionally only output the error info per each failed font at a
raised verbosity level of >=4 to avoid too much clutter if many fonts
fail. This is important for 32-Bit builds of PTB where the
FMGetFontFamilyName() fails quite frequently for a couple of default
fonts on modern OSX versions, so we want to reduce clutter, as the
failure can only be fixed by switching to 64-Bit PTB anyway.

Should solve issue reported in ptb forum message #16109, at least once
this is merged into the 3.0.10 legacy branch.

-> Verified on 64-Bit PTB that the change compiles and doesn't
introduce new obvious issues.
Screen for 32-Bit Matlab on OSX rebuilt with font enumeration fix.

To make warnings about defective fonts less chatty.