Simply disallow it, just as we disallow creation of routines from within
other SPs.


include/mysqld_error.h:
  New error code for when attempting to drop a stored routine from within
  another stored routine.
mysql-test/r/sp-error.result:
  New test case for BUG#4344.
mysql-test/t/sp-error.test:
  New test case for BUG#4344.
sql/share/czech/errmsg.txt:
  New error message for when attempting to drop a stored routine from within
  another stored routine.
sql/share/danish/errmsg.txt:
  New error message for when attempting to drop a stored routine from within
  another stored routine.
sql/share/dutch/errmsg.txt:
  New error message for when attempting to drop a stored routine from within
  another stored routine.
sql/share/english/errmsg.txt:
  New error message for when attempting to drop a stored routine from within
  another stored routine.
sql/share/estonian/errmsg.txt:
  New error message for when attempting to drop a stored routine from within
  another stored routine.
sql/share/french/errmsg.txt:
  New error message for when attempting to drop a stored routine from within
  another stored routine.
sql/share/german/errmsg.txt:
  New error message for when attempting to drop a stored routine from within
  another stored routine.
sql/share/greek/errmsg.txt:
  New error message for when attempting to drop a stored routine from within
  another stored routine.
sql/share/hungarian/errmsg.txt:
  New error message for when attempting to drop a stored routine from within
  another stored routine.
sql/share/italian/errmsg.txt:
  New error message for when attempting to drop a stored routine from within
  another stored routine.
sql/share/japanese/errmsg.txt:
  New error message for when attempting to drop a stored routine from within
  another stored routine.
sql/share/korean/errmsg.txt:
  New error message for when attempting to drop a stored routine from within
  another stored routine.
sql/share/norwegian-ny/errmsg.txt:
  New error message for when attempting to drop a stored routine from within
  another stored routine.
sql/share/norwegian/errmsg.txt:
  New error message for when attempting to drop a stored routine from within
  another stored routine.
sql/share/polish/errmsg.txt:
  New error message for when attempting to drop a stored routine from within
  another stored routine.
sql/share/portuguese/errmsg.txt:
  New error message for when attempting to drop a stored routine from within
  another stored routine.
sql/share/romanian/errmsg.txt:
  New error message for when attempting to drop a stored routine from within
  another stored routine.
sql/share/russian/errmsg.txt:
  New error message for when attempting to drop a stored routine from within
  another stored routine.
sql/share/serbian/errmsg.txt:
  New error message for when attempting to drop a stored routine from within
  another stored routine.
sql/share/slovak/errmsg.txt:
  New error message for when attempting to drop a stored routine from within
  another stored routine.
sql/share/spanish/errmsg.txt:
  New error message for when attempting to drop a stored routine from within
  another stored routine.
sql/share/swedish/errmsg.txt:
  New error message for when attempting to drop a stored routine from within
  another stored routine.
sql/share/ukrainian/errmsg.txt:
  New error message for when attempting to drop a stored routine from within
  another stored routine.
sql/sql_yacc.yy:
  Don't allow drop function/procedure from within another function/procedure.