Fix up shader errors messages with full path
Fix up shader errors messages with full path

Errors coming from the compiler only include the string used to include
a file, not the full path. Use a bit of regex to fix that. Errors from
included files and the primary file are now consistent. As a bonus,
custom downsample errors don't say "_scriptDownsample" everywhere!

simontaylor81/Syrup,simontaylor81/Syrup