replace "dot" with "set not containing whitespace"

Fixed issue in lexer in the same category as that of :ticket:`366` where
the regexp used to match an end tag didn't correctly organize for matching
characters surrounded by whitespace, leading to high memory / interpreter
hang if a closing tag incorrectly had a large amount of unterminated space
in it. Credit to Sebastian Chnelik for locating the issue.

As Mako templates inherently render and directly invoke arbitrary Python
code from the template source, it is **never** appropriate to create
templates that contain untrusted input.

Fixes: #367
Change-Id: I2f3a8665e92c1b6efcf36b1dba6e58fe0975b7da
4 files changed