Fix the build with gcc 4.2 and clang.

The Nepomuk2 and Nepomuk2::Query namespaces are included, which causes some
ambiguity in the `query' argument of intiWatcherForQuery(), which can be
expanded as both Nepomuk2::Query::Query (from libnepomukcore/query/query.h)
or Nepomuk2::Query (from libnepomukcore/query/negationterm.h).

Meanwhile, this was fixed in master by someone else who didn't fix the
KDE/4.9 branch (see eaeae8d1).

CCMAIL: nepomuk@kde.org