improve dojo.string.trim()

[guest]

Refs #3731.

Actual dojo.string.trim() implementation comes from a Steven Levithan's post.

Steven Levithan has added to his post about trim (http://blog.stevenlevithan.com/archives/faster-trim-javascript) a faster and shorter implementation (the 12th, he calls it trim12). I think dojo.string.trim() should be updated with that implementation.

[wolfram]

If there is already movement in dojo.string.trim(), let me suggest another addition, that many of the default trim implementations (i.e. Python) have, it is passing a second parameter of which string to trim, like so:

>>> dojo.string.trim("/path/to/split/", "/")
"path/to/split"

>>> dojo.string.trim("DELIM what the heck DELIM", "DELIM")
" what the heck "