mesa: change ctx->Driver.ProgramStringNotify() to return GLboolean

mesa: change ctx->Driver.ProgramStringNotify() to return GLboolean

GL_TRUE indicates that the driver accepts the program.
GL_FALSE indicates the program can't be compiled/translated by the
driver for some reason (too many resources used, etc).

Propogate this result up to the GL API: set GL_INVALID_OPERATION
error if glProgramString() was called.  Set shader program link
status to GL_FALSE if glLinkProgram() was called.

At this point, drivers still don't do any program checking and
always return GL_TRUE.