Added .gitignore
[FEATURE] Support for multiple TYPO3 instances

This patch adds another header TYPO3-Sitename to each page, so varnish can differ between different TYPO3 instances.
[FEATURE] Added configuration option to always send TYPO3 headers

Added an extension configuration option to force TYPO3 to output the TYPO3 Pid and Sitename headers. This can be useful, if the backend webserver is behind multiple proxy servers.
[TASK] Added new static method tx_varnish_GeneralUtility::getSitename()
Merge pull request #4 from derhansen/master

Support for multiple TYPO3 instances and new option in extension config