* Makefile:
  . Add s_erfl.c to building libm.
  . Add MLINKS for erfl.3 and erfcl.3.

* Symbol.map:
  . Move erfl and erfcl to their proper location.

* ld128/s_erfl.c:
  . Implementations of erfl and erfcl in the IEEE 754 128-bit format.

* ld80/s_erfl.c:
  . Implementations of erfl and erfcl in the Intel 80-bit format.

* man/erf.3:
  . Document the new functions.
  . While here, remove an incomplete sentence.

* src/imprecise.c:
  . Remove the stupidity of mapping erfl and erfcl to erf and erfc.

* src/math.h:
  . Move the declarations of erfl and erfcl to their proper place.

* src/s_erf.c:
  . For architectures where double and long double are the same
    floating point format, use weak references to map erfl to
    erf and ercl to erfc.

Reviewed by:	bde (many earlier versions)