Generic highlighter: New option to specify ignored file patterns so the highlight popup does not show up.

This should speed things up a bit, because before, the line was tokenized at
least 3 times.

Generic highlighter: Fix to correct storage of block states when leading context sequences are nested with persistent contexts.

This situation is represented by case 5 of testPersistentContexts from the highlighter engine unit tests.

Reviewed-by: erikv

Reviewed-by: Oswald Buddenhagen

In theory this should have been a backport of the search-related commits
7e8c345a and 46fa3aa7, but they are buried in the middle of the Big
Commandline Reorganization. Just taking everything has lower risk and
is faster.

that way the result vector can be pre-allocated - which gives zero
resizes if no expansions are in the expression.
for the joined argument lists of built-in functions, pre-allocate a
fixed 5 elements, which covers all cases and more.
the argument lists of user-defined functions are not pre-allocated
yet.

this gives a rather significant boost, in particular for
expressions which are evaluated repeatedly (includes).

some replace functions can return empty elements which should be
zapped here (according to qmake, anyway).

this saves quite some mallocs in the parsing pass.

it's private to ProFileEvaluator::Private since the getting rid of
the visitor pattern.

ProString is almost a QStringRef, except that it keeps a copy of instead
of a pointer to the QString - to make it refcountable. additionally, it
holds a hash so it can be efficiently used for repetetive hash lookups.

this function class just joins each string list argument into a
single string. so instead of first building a list and joining it
right afterwards, create a single string in the first place.

that's actually kinda braindead, but that's qmake as usual.