remove adapter from extensions/storage/filesystem/adapter

- it is not used
- the one in extensions/adapater/storage/filesystem is enhanced
Add exists functionality / merge almost identical SystemWrite/SystemRead test

As the SystemWrite and SystemRead test are almost identical, they are merged
into one SystemActions (including a test for the exists)
Merge branch 'add_exists'

Conflicts:
	tests/integration/extensions/storage/FileSystemTest.php
	tests/integration/storage/FileSystemTest.php
Merge branch 'fix_double_adaptor'

Conflicts:
	tests/cases/extensions/storage/filesystem/adapter/FileTest.php
gitignore eclipse
using clearstatcache w/o specifying a file has performance considerations