fix buffer overflow for unknown mode numbers

to test, try /mode 1337 ; map ac_desert
replace textfilter functions with one-fits-all version

* replaces filtertext() with a version with a dozen of single filters
  that can be used in any combination
* defines classes of allowed characters for strings for various uses
  (see protocol.h line 153ff)
* now the allowed charset of, for example, player names is defined
  in one location only
* fixes issue #58
play drop sound when exiting edit mode

...and the player "drops" back into the map
(fixes issue #55)
fix: don't apply water physics in edit mode

* no longer slows down the player under water
* no longer plays sounds for water transitions
* still plays underwater sound and shows underwater visual effects

fixes issue #56
fix: don't play hard landing sounds on water transitions

fixes issue #57
fix: keep path and uppercase in demo filenames

votes now distinguish between demo and map votecalls and filter the
filename appropriately

also: remove paths from map names cleanly
fix failed assertion on making selections in editmode

last() may not be used on an empty vector

also, the FIXME was obsolete, since addselection() does call correctsel()
Moving the clock on the top right.

See: http://i.imgur.com/20MXPSI.jpg