Prefer boost::mutex to std::mutex as they are not implemented in MinGW

* We are in 2014 and it is C++11, sigh.
* Also fixes a mismatch.
Merge pull request #194 from eregon/boost_mutex

Prefer boost::mutex to std::mutex as they are not implemented in MinGW
Rename bootunpickler-decl.hh to bootunpickler.hh

* It is included in mozartcore.hh and has its own .cc.
* There was no bootunpickler.hh but one bootunpickler.cc.
* The interface only needs to be declared at .hh level.
Allow Oz to use the efficient boot unpickler
Implement unpickling of unicodeString in bootunpickler

* Also add an error message when type is unknown.
Fix unpickling of namedname
Fix missing argument in MemManagedList::remove_after()

* Also document usage of remove().