geshifilter 5.x-2.1

Main changes since version 5.x-2.0:

• Added a submodule with a GeSHi source code node type
• #178310: enables highlighting of source code, when teaser view trims inside source code and there is consequently no closing </code> tag
• #179077: usage of pretty language name where possible (e.g. "C++" instead of "cpp")
• added hook_requirements() hook for showing GeSHi library problems and filter conflicts on the status report page
• #181402: GeSHi filter now includes a prepare phase for escaping the source code container tags and its content. This removes conflict issues with HTML filter for example. Thanks to aclight.
• added codefilter conflict detection
• made it possible to nest [code] and <code> tags
• various bug fixes and tweaks