squash! WIP WebCLImageSamplerSafetyHandler
WebCLFunctionCallHandler: generalized from WebCLBuiltinHandler

Now the matching of operations to perform is done by function call
expression instead of only its name part. This reduces the efficiency
a bit as the list of wrapper functions needs to be iterated instead of
accessed directly by the name, but it also adds the ability to perform
function call wrapping by some criteria other tha the function
name. Such would be the case of wrapping all function calls involving
sampler_t.
WebCLKernelHandler::run: eliminated an unused variable that produced a warning
WebCLTransformer: added a general sampler_t handler that wraps all function calls involving sampler_t