Merge pull request #40 from ntd/pr6

Use SHA1 from LuaCrypto, if available
Merge branch 'upstream'
force busted 1.11

busted 2.0 has changed async test interface
server_copas: code cleanup

on_error is valorized at line 56: no need to check for it before every
call.
server_copas: more descriptive errors
Merge branch 'pr7'