Kevin Haller authored Sep 13, 2015 and Carlos Garnacho committed May 08, 2016

Extends the sqlite database by a new function (with the name
SparqlReplace). The function makes use of the g_regex_replace() function
of glib.

To fullfill the XPath 2.0 standard some constraints must be checked for
fn:replace(input, pattern, replacement, flags). The given pattern must
not match a zero-length string. The given replacement string have to use
$ followed by a number for backreferences. If the dollar sign shall be used
"as is", it must be escaped (\$).

For checking and interpreting the given replacement string of fn:replace()
some regular expressions are needed. This expressions are precompiled and
saved in the function_regex hashset of the TrackerDBInterface. The
pre-compilation and initialization of the hashset are done by the
prepare_database() method.

The glib method g_regex_replace() make use of the backslash followed by a
number to inidcate backreferences. So the dollar signs must be interpreted
- the backslashes can be still used for this purpose.

In the sparql expression class the corresponding section is adapted, so
that the new SparqlReplace function is used for fn:replace(..) statements.

https://bugzilla.gnome.org/show_bug.cgi?id=754961