[ticket/10970] Paths of the form {FOO}/a/{BAR}/b parsed correctly

A new method to handle this type of path was added and
compile_tag_include, compile_tag_include_php and
compile_tag_include_js were modified to use it appropriately.

Tests were added for these three macros also.

PHPBB3-10970

tests/template/templates/includejs.html

@@ -2,4 +2,6 @@
 <!-- INCLUDEJS {PARENT} -->
 <!-- DEFINE $TEST = 'child_only.js' -->
 <!-- INCLUDEJS {$TEST} -->
-{SCRIPTS}
+<!-- INCLUDEJS subdir/{PARENT} -->
+<!-- INCLUDEJS {SUBDIR}/subsubdir/{PARENT} -->
+{SCRIPTS}