Fix #887: Use ly:string-percent-encode for textedit URIs. (issue193077)

[lemzwerg]

http://codereview.appspot.com/193077/diff/1001/12
File lily/general-scheme.cc (right):

http://codereview.appspot.com/193077/diff/1001/12#newcode230
lily/general-scheme.cc:230: return ((c >= 0x2D && c <= 0x2F) // hyphen,
full-stop, and forward-slash
Wouldn't it be faster to use an array of `0' and `1', indexed by the
character code, instead of the many comparison operations?  E.g.

  escape_character[128] = { 0, 0, 0, ..., 1, 1, 0, ... }

http://codereview.appspot.com/193077/show