Fixed #8404 -- Isolated auth password-related tests from custom templates
Fixed a misnamed variable introduced in commit 142ec8b283

Refs #8404.
Fixed #19819 - Improved template filter errors handling.

Wrap the Parser.compile_filter method call with a try/except and call the
newly added Parser.compile_filter_error(). Overwrite this method in the
DebugParser to throw the correct error.

Since this error was otherwise catched by the compile_function try/except
block the debugger highlighted the wrong line.
Fixed #19823 -- Fixed memcached code example in cache docs