Performance Part #1

Remove unused functions. Replace all file_exists with is_file. Fix
Exception constructor again (sorry, first time working with github).
Introduce STRLEN constants, to remove the strlen call on constant
values.
Performance Part #2

Remove unused property. Fix constant call in content node. Removed
unused code in DirectiveNode. Remove identify problem for the foreach
context variable $selector in RuleNode. Remove unreachable throw
exception call. Init $tokens in lexer. Create used SassListException.
Part #3

Remove strlen on constants (one more). Replace all is_null with the PHP
construct „ === null“. Replace magic calls (overhead with ucfirst and
method_exists) with direct getter-calls. Remove strlen call in for-loop
in SassList::_build_list.
Merge pull request #152 from lochmueller/performance_cleanups

Performance cleanups
fix for fatal error "Call to undefined method SassMixinNode::resolveSelectors() in tree/SassExtendNode.php on line 49" when using @extend as an immediate child of a mixin (see test case).
Fix for issue #71 . Variables in directives in mixins don't work the second time the mixin is used
Merge pull request #153 from gabrielfin/bugfix-extend

fix for fatal error when using @extend as an immediate child of a mixin
Merge .gitignore
@extends in rules of 2 o more levels deep were always ignored
Update Compass.php

Fix for Windows-Server:
replacing backslash with slash.
Merge pull request #155 from gabrielfin/fix-extend-nested-import

@extends in rules of 2 o more levels deep were always ignored
Merge pull request #156 from SourceR85/patch-1

Update Compass.php