Fix a Rails perf issue.

Closes #124.
Implement sourcemap generation
Remove unnecessary code, add files that were left behind
Fix line counting in the sourcemap output
Follow review, remove unnecessary :id field and an unused method
Add a `--poll` command-line flag to force a polling backend.

Closes #504
Print a warning for ambiguous @imports.

Closes #499
Merge branch 'stable'
Consider files with the same name to be an error.

See #499
Make sure @import errors have the correct line and file info.
Support protocol-relative URLs.

Closes #508
Merge branch 'stable'
Merge branch 'master' into sourcemap

Conflicts:
	lib/sass/scss/parser.rb
Changes to the structure and style of the source map patch.
Fix some off-by-one bugs in column calculations.
JSON dumping tests added, json_value_of return type and whitespace character dumping fixed
Merge pull request #524 from crdev/sourcemap

JSON dumping tests added, return type and special character escaping fixed
Add line numbers and file names to eval calls.

Closes #528
Get rid of Sass::Util.char_size.

This was causing as many problems as it fixed, since it didn't address other
byte-indexed methods on 1.8 (e.g. String#[]). Avoiding byte indexing pervasively
would be more effort than it's worth.
Rename SourceMapping to SourceMap.