fix pragma to allow tabs for whitespace

+ Uses the more permissive regexp symbol \s to denote whitespace instead of literal whitespace, this way, tabs in the #pragma directive won't trip up the shader includes preprocessor.
remove unnecessary glGet

+ glGet() directives stall the GL pipeline by implicitly flushing the command buffer and should not be used in the draw loop.

+ I've tested performance on this with Nsight and it seems that the earlier claim for better perf is outdated, especially when GPU-CPU asynchronicity and best possible GPU load balancing is desired.
add printout for offending shader source

+ adds printout for offending shader lines if shader compilation returns an error:

as soon as a shader uses the #pragma include directive, line numbers were off by whichever number of lines the include injected into the current shader source.

by printing out the offending line as it appears in the current shader source with a couple of lines of context, errors can be found more reliably
Merge pull request #3164 from tgfrerer/fix-ofShader-error-log

Small fixes to ofShader