Log Message:
Update to orpie-1.5.0 and add DESTDIR support.

ChangeLog:
- Complete rewrite of units implementation, allowing user-defined units
  and physical constants.
- Updated included ocamlgsl bindings to 0.6.0.
- Square root of a negative value now returns a complex result.
- gcd(), lcd(), and mod() now accept real-valued  arguments.
- Fix for crash in abbrev mode.
- Made a minor Makefile change to correct linking errors under Gentoo
  (maybe others).
- Numerous code cleanups. Calculator code has been better separated from
  interface code.
- Support --sysconfdir configure option.  (Anyone packaging for the
  filesystem hierarchy standard will now need to use something like
  "./configure --prefix=/usr --sysconfdir=/etc".)
- Implemented entry of most fundamental physical constants.
- Fixed incorrect error message regarding deprecated extended_enter command