Update MemcacheEngine.php

adding $limit=0 to clear function so it deletes all the keys for real
Mark compatibility shims as deprecated.

Fixes #2845
Update MemcacheEngine.php

removing variable assignment
Merge pull request #2852 from ujwaltrivedi/master

Update MemcacheEngine.php
Update MemcacheEngine.php

removed 0 from getExtendedStats('slabs') in my last commit, someone point that out in the comment. Adding it back.
Merge pull request #2861 from ujwaltrivedi/master

Get unlimited number of slabs when clearing cache keys in memcache.
Fix Validation::decimal() not working with localized floats.

Use similar workarounds as DboSource::value() for accepting localized
floats.

Fixes #2853
account for localized floats more robustly.

Normalize floats, strings too, so that they are validated as

    dddddddddd.dd

ref #2853
Merge pull request #2864 from AD7six/2.4-better-float-validation

account for localized floats more robustly.