Use package gorp instead of gorp_test to eliminate need to change files ...

Changes `gorp_test.go` to use package gorp instead of gorp_test to eliminate the need to change the source in forks or when importing from different path. (I.e., I fork to github.com/foo/gorp.git, and then I have to be sure to change the import path in `gorp_test.go` to use my fork, or else I'll just be testing the coopernurse/gorp code.) This requires renaming a few functions that collide with functions defined in `gorp.go`.