Make all the easy updates. There are still quite a few to do, but in
doing these ones I can see that syntastic#makeprg#build() needs to
accept a few more options. Namely:
* "postargs" that appear after the filename
* "tail" that appears after everything - used for things like
redirecting output and piping to grep/sed/etc
* the filename itself - only the java checkers needed this since they
specify the directory of the file to check as well
There are still a few other things to do as well:
* remove the options from the checkers that are now provided by
syntastic#makeprg#build implicitly - i.e. the checker exe and args.
* also, we need to doc the above implicit checker options
Previously, if we edited a new bash script then we would have to wipeout
the buffer and recreate it to get syntastic to recognise it as a bash
script. This is because it parsed out a magic number and cached that -
and it trivially fails to find a magic number when you create a new
file.
So recheck for a magic number if it is currently empty.
Also, do a small refactor.
