Stop exporting the not implemented CompressedFile in Open.oz

* The ZlibIO boot module is not yet implemented.
* A few scripts (Pickler.oz, Executor.oz) check
  {HasFeature Open compressedFile},
  so now they should behave properly as it is not defined.
Merge pull request #189 from eregon/zlibio

Stop exporting the not implemented CompressedFile in Open.oz
Load Pickle in the VM module in VM.getPort and VM.new.

* So it is only loaded when we are about to need it
  (we cannot easily load it in Send).
* If someone uses a reference to VM.getPort, then passing it around
  carries the dependency on Pickle, which is necessary.
* Messages sent to monitor streams are fine as they do not need Pickle.
Merge pull request #190 from eregon/mvm

Load Pickle in the VM module in VM.getPort and VM.new.
Add Boot_Time.getMonotonicTime for benchmarking purpose

* The unit is the nanosecond and it uses a monotonic clock,
  C++'s steady_clock.
* It is slightly expensive on 32-bit as it will return a BigInt.
Merge pull request #191 from eregon/monotonic_time

Add Boot_Time.getMonotonicTime for benchmarking purpose
Add a test for VMPort's type
Synchronize calls using the environment variables

* As the underlying C functions are not thread-safe.
* See http://en.cppreference.com/w/cpp/utility/program/getenv.
Merge pull request #192 from eregon/mvm

Make environment variables thread-safe
Added the debugEntry op codes, and let the StackTrace use them.

This is mainly to make `ozc -g` work and reports more accurate line numbers
on crash.
Merge pull request #193 from kennytm/debug-entry

Make `ozc -g` and stack traces work
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
Ensure to release the VM list mutex before destroying the environment
Merge pull request #195 from eregon/mvm

Ensure to release the VM list mutex before destroying the environment