Revert "rustboot: Emit an error instead of asserting in trans when a T is passed by value" due to test failures

This reverts commit ee901858.

On gcc 4.5.1 (fedora 14 i686) rust_test_runtime.cpp fails to compile
with the following error:

  rt/test/rust_test_runtime.cpp:57:61: error: passing NULL to non-pointer argument 3 of ‘void rust_task::start(uintptr_t, uintptr_t, uintptr_t, size_t)’

The explicit cast works around the error.

Emit a sensible error message if one or more of the parameters isn't enough context to instantiate a polymorphic function

rustboot: Emit an error message instead of asserting on a type-param mismatch in tag constructors in patterns

rustboot: Use a less hacky method to report tag names in error messages, which works for resolve errors as well

Prevent Not_found in the unfortunate case when we have to "friendly_stringify" a tag type we haven't yet recorded into cx.ctxt_all_tag_info

Pass outptr as in rustboot. Probably need to revisit this ABI. Also disgusting hack employed. Please remove.

rustboot: If the user tries to instantiate a non-parametric type with type parameters, report the location of the error

(cherry picked from commit 11d2af72cf956cc28549cfd280ba40de1645eee7)

This change is thanks to Peter Hull, who independently resolved
the 2.8 vs 2.8svn issue this way. His patch checked the version
string against a fixed set of options, which is easier to read
and simpler to adjust in the future.
(cherry picked from commit 83cc297561a78ad13fcd1c2943f17ace81c725b8)

Ubuntu ships the llvm bindings in /usr/lib/ocaml/llvm/ but Fedora
is installing them directly in /usr/lib/ocaml so we need to check
there as well.

The patch is untested; Fedora 14, the current beta, includes llvm 2.7.
It does add an unnecessary -I directive, but should at least have a
better chance of working on Fedora 15.
(cherry picked from commit 8af7360bd3de851668a133ae6ba4419e3722c6aa)