Removing test for bug #2080.

Naming a Ltac definition like a built-in tactic used to fail, but now only
spits out a warning. This is too complicated to test...
coq_makefile: build and install *top.cmxs plugins

These plugins, like coqidetop, stmworkertop and tacworkertop are
intended for toploop replacements (see -toploop command line option).

With this commit coq_makefile can be used as the build system for
any user-interface-specific plugins.
Add additional location information to AST XMLs.
Factored out IDE goal structure.

The more structured goal record type of CoqIDE is also useful for other
interfaces (in particular, for PIDE). To support this, the datatype was
factored out to the Proof module. In addition, the record gains a type
parameter, to allow interfaces to adapt the output to their needs.

To accommodate this type, the Proof module also gains the
map_structured_proof that takes a Proof.proof and a function on the
individual goals (in the context of an evar map) and produces a
structured goal based on the goal transformer.
STM: report the (structured) goals as XML

The leafs of the XML trees are still pretty-printed strings, but this
could be refined later on.