Support watchify pipe output option

[Izhaki]

The watchify docs say:

--outfile=FILE, -o FILE

This option is required. Write the browserify bundle to this file. If
the file contains the operators `|` or `>`, it will be treated as a
shell command, and the output will be piped to it.

Problem is that if you provide the outputfile something like the examples given

-o 'exorcist static/bundle.js.map > static/bundle.js'

globify does not recognise it as such and creates a folder instead.

[JamesMessinger]

This is related to Issue #11, since supporting output to stdout would also support piping to other programs.