Uses Error.stack to know where db.load was called from and pushes cwd from it

Otherwise it reverts to process.cwd. It also appends "index" to path if
path is a folder.
Changes db.load to avoid throwing and just create the error

Duh..
Adds test for db.load()
Merge pull request #63 from dresende/db-load

db.load() behaving just like require()