compile_tag_if had the flawed approach of adding an isset statement for
all variables to the beginning of the if. This fails for negative
expressions, and checking those takes a considerable effort.
The easier solution is to make the variable expression itself
conditional, defaulting to null if it is not set.
Thanks to naderman for the solution.
PHPBB3-9726
This error resulted in a dot from the namespace being placed into
variable reference in compiled template code, thus creating bogus
compiled template code.
PHPBB3-9726
phpbb_template_compile is now much simpler. It takes complete file paths
as inputs, either source template path or source template path and output
compiled template path. The number of methods also went down to two -
compile template and returned compiled text or compile and write to file.
phpbb_compile class is responsible for determining source and compiled
paths. It already had all the data necessary for this, now the code is
in the same place as the data it uses.
PHPBB3-9726
