Remove the NetBSD setexception changes on the master branch. This is
only for the upcoming release.
Fix error in type derivation for the sign in DECODE-FLOAT.

Type derivation of the sign of (DECODE-FLOAT X) returned the incorrect
value when x was declared to be of type (DOUBLE-FLOAT (0d0)).

 * src/compiler/float-tran.lisp
   * Fix type derivation
 * tests/float-tran.lisp
   * New file for tests of DECODE-FLOAT-SIGN-DERIVE-TYPE-AUX.
 * tests/float.lisp
   * New file to test that decode-float is compiled correctly.
Fix type derivation of the exponent for DECODE-FLOAT.

The minimum exponent is from 0, it's from least-positive float.

 * src/compiler/float-tran.lisp:
   * Derive the correct minimum exponent by using the exponent from
     the least-positive float value of the appropriate type.
 * tests/float-tran.lisp:
   * Add tests for the derived exponent type for DECODE-FLOAT.

Conflicts:
	tests/float-tran.lisp