Many of the syntax checkers were setting the 'bufnr' key for each
error manually and one was setting 'text' if it didnt exist too.
Add the 'defaults' option to SyntasticMake to set default values in the
returned error list - it only sets values if they are empty.
This was missing errors like this:
/tmp/foo.js:1:(-002) Error parsing file at token ")". Unable to check the rest of file.
The reason is because of the minus sign in front of the 002. It is using
%m to match that, which appears to only match positive numbers - so just
ignore the minus sign.
Add the g:syntastic_javascript_checker option so the user can specify
which javascript syntax checker to use. If none is specified then just
use the first syntax checker we find installed.
