Fix crash on searching.

I have moved page_id lookup to the line before the if block
where we construct the search page result. So when we lookup for
the document content using the page_id, it's available and the program
doesn't throw a segmentation fault.

https://bugzilla.gnome.org/show_bug.cgi?id=736312
yelp-window: Style the find revealer

https://bugzilla.gnome.org/show_bug.cgi?id=736408
tests: Port from GtkVBox and GtkHBox to GtkBox

https://bugzilla.gnome.org/show_bug.cgi?id=670180
libyelp: Make some private functions static

https://bugzilla.gnome.org/show_bug.cgi?id=720577
icons: Use bookmark icon from theme

The icon naming specification provides for a user-bookmarks icon, which
fits well with both yelp-bookmark-add-symbolic and
yelp-bookmark-remove-symbolic, which were not used as action icons
anyway.

https://bugzilla.gnome.org/show_bug.cgi?id=734165
Use more stringent configure flags for distcheck

As both bzip2 and lzma support are required for building the
documentation during distcheck, add the relevant arguments to
DISTCHECK_CONFIGURE_FLAGS.