Add a script to generate test coverage report.
Add a script to generate test coverage report.

This commit adds a script which can be used to generate the test coverage
report.  It detects whether or not gcc is installed and adds the necessary
build tag to enable the new cgo tests when gcc is available.

bparees/go-spew,davecgh/go-spew,kortschak/utter,FactomProject/go-spew,dvln/go-spew,davecgh/go-spew,bparees/go-spew,FactomProject/go-spew,dvln/go-spew