[vile] TCL highlighting

[Wayne Cuddy]

I may have found a minor bug in the syntax highlighting for TCL. This
has to do with TCL commands interpolated inside string literals.

So this works as expected:

tcl_command "string literal arg"

This does not:

tcl_command1 "string literal arg [tcl_command2 "args to cmd2"]"

The literal highlighting for tcl_command1 stops at the second '"'
character. I suppose it's subjective as to if it should stop at the
4th '"' or the first '['.

It would be nice if it stopped at the '[', parsed the content between
the '[' and ']' as a command and continued the string literal after
the ']' up to the closing '"'.

Wayne