Trigger citation completion on \Cite as well as \cite.

This is useful for BibLaTeX users, where there is a \Cite* family of commands.
Fix #9 restoring of cwd

The s:origdir variable was local to the source file. Since all functions used
the same name for the variable to save the old working directory, restoring did
not work with nested function calls as one call would overwrite the restore
value of a function invocation higher up the stack.

This was fixed by replacing s:origdir with a local variable l:origdir
Reverted changes from kaihowl in texviewer.vim