http-interface: - fixed large playlist loading failure
http-interface: - fixed large playlist loading failure

large playlists can take >10 seconds to load. since the xmlhttp object is
common within the page, multiple /status.xml requests would occurr (1 per sec)
before the playlist was loaded cancelling the /playlist.xml request.. i moved
the xmlhttp request object to a global variable. it's now checked to see if
there are any outstanding/active requests before submitting a new request. -
improved playlist display of large playlists.

Signed-off-by: Ilkka Ollakka <88b345e2e0969920adc1eaa21d1a29b223865bcf@videolan.org>

shyamalschandra/vlc,vlc-mirror/vlc-2.1,krichter722/vlc,shyamalschandra/vlc,shyamalschandra/vlc,jomanmuk/vlc-2.2,jomanmuk/vlc-2.1,krichter722/vlc,jomanmuk/vlc-2.2,vlc-mirror/vlc,xkfz007/vlc,krichter722/vlc,jomanmuk/vlc-2.1,xkfz007/vlc,shyamalschandra/vlc,vlc-mirror/vlc-2.1,jomanmuk/vlc-2.1,shyamalschandra/vlc,krichter722/vlc,jomanmuk/vlc-2.2,vlc-mirror/vlc,jomanmuk/vlc-2.1,jomanmuk/vlc-2.2,vlc-mirror/vlc-2.1,vlc-mirror/vlc,vlc-mirror/vlc,xkfz007/vlc,vlc-mirror/vlc-2.1,xkfz007/vlc,vlc-mirror/vlc,jomanmuk/vlc-2.2,xkfz007/vlc,vlc-mirror/vlc-2.1,xkfz007/vlc,vlc-mirror/vlc,jomanmuk/vlc-2.1,shyamalschandra/vlc,shyamalschandra/vlc,krichter722/vlc,vlc-mirror/vlc-2.1,vlc-mirror/vlc-2.1,jomanmuk/vlc-2.1,jomanmuk/vlc-2.1,jomanmuk/vlc-2.2,vlc-mirror/vlc,krichter722/vlc,xkfz007/vlc,jomanmuk/vlc-2.2,krichter722/vlc