Fix an issue when busted is called with -o

* This change makes sure opath is not nil

* When trying busted -o some/output.lua, busted was failing with:

Busted process errors occured / Unable to open output module; requested option '--output=some/output.lua'.
$HOME/.luarocks/share/lua/5.1/busted/core.lua:67: $HOME/.luarocks/share/lua/5.1/pl/path.lua:233: argument 1 expected a 'string', got a 'nil'
Added multiplatform CI testing
Use scm version of lua-ev
Adapted command-line spec to the pl issue
Merge pull request #219 from mpeterv/multiplatform_testing

Multiplatform testing
Merge pull request #216 from losinggeneration/master

Fix an issue when busted is called with -o my/output.lua
use `string.len` instead of `#` on async trace test
Merge pull request #226 from Olivine-Labs/fix-async-test

use `string.len` instead of `#` on async trace test
add travis badge again
Update README.md
Update README.md
renamed bootstrap
Fixes #227, closes #224 and fixes #228
Merge pull request #234 from Tieske/master

removes -l option
version 1.11.0
Add language th -- Thai Language
Merge pull request #237 from narate/add-language-th

Add language th -- Thai Language
Revert "Fixes #227, closes #224 and fixes #228"

This reverts commit e3c54c58b47ee390276a1350f129d811012a0816.
Revert "renamed bootstrap"

This reverts commit 7730904e9338411bce75ceeb97ac498b98b3f3d7.
Revert "Merge pull request #234 from Tieske/master"

This reverts commit 7179c92915d14106f071fd6738fc2d1a9ab02a8a, reversing
changes made to 6ac24b040d8b89c1f31282b6a674b8770db2fdfa.