Allow configuration of asynchronous XHR

Set less.async and/or less.fileAsync to true before including less.js to
force asynchronous XHR requests to be used.  fileAsync is introduced
as a separate setting to maintain existing semantics, as previously changing
less.async to true would only affect http protocol XHRs.
Check XHR return type appropriately

Asynchronous file XHRs need to listen for onreadystatechange.
Added ruleset source line number dumping support for debugging purposes.
New line is now only inserted between rulesets when not in compress mode.
Unit tests for debug numbers
Updated .gitignore (for emacs)
Added media query support.

 * env.dumpLineNumbers was being lost when doing "offline" compilation
   (within node.js)
 * Added documentation for the changed options
 * --line-numbers now takes a parameter
   (either "comments", "mediaquery" or "all")
 * The system can now again output mediaqueries for FireLESS
 * Moved comments tests in debug/comments, will duplicate
   for mediaquery and for "all"

Everything is still utterly broken though, tests still fail.
Fixed some tests.

 * Import filenames are okay, line numbers are off by one in some cases
 * The nested media query still makes .tst show up as undefined
Fixed debug info test (with comments).

Some line numbers were incorrectly off-by-one.
getLocation() seems to return lines starting at 0, therefore we have to add 1.

This fixes the off-by-one bug,
and is consistent with what is done at line 238 in 'parser.js'.
Removed the passing around of an env.filename that is wrong when doing imports.
Wrapped ruleset debug info passing in condition.
Fixed nested media bug.
Completed tests.

Made a minor modification to the test runner to best reuse tests
in these cases.
Fixed path replacements in text a little bit better.
Minor fixes.

Fixed a bug that could appear with compression enabled,
and minor tabbing issues in tests.
(dist) build 1.3.1
update changelog for 1.3.1
alternative to throwing an object literal.

create a real exception and extend it with the
custom properties that less needs to satisfy its
error generator. An alternative to the solution
proposed in cloudhead/less.js#963
Fix problem with name arguments with arguments variable and if you've specified all the arguments