Clearer error messages when audio open fails

The existing chain of errors from all providers can be really confusing,
so instead try to interpret the exception type to add some meaning.
Remove whitespace in MSYS shell environment vars

It seems that whitespace around the paths in the PATH, LIB, INCLUDE env
vars can break in some situations, making the build fail entirely.
Unfortunately this also makes the file harder to read and diff.
Add user *.props files to gitignore