Fix a compilation failure on svref of a symbol macro

 Introduced in 0892423b (faster SVREF and (SETF SVREF) compilation)

 Thanks to James M. Lawrence for the quick report, with a reduced
 test case.
Stop emitting references to inexistant #n= forms in the pretty printer

 * Special logic was introduced in 2003 to avoid pprinting backquote-comma
   forms as ", foo" when ",foo" is unambiguous; the bug has likely been
   around since then.

 * Reported by Douglas Katzman on launchpad, and reduced by James M. Lawrence
   (lp#1161218)
type=: Compare &key parameters of function types.

Compare key parameters in type=-args, mostly so that deftransforms
with key arguments could be redefined at runtime.
Check bounds of ELT on &more in safe code.

Disable &more optimizations for ELT if safety = 3.