avoid redefinition of OroGen::TypekitMarshallers

orogen.rb was defining it (with logger and backward
compatibility definition) but it was really the job
of orogen/marshallers
test: migrate tests to minitest
test: require minitest/autorun in orogen/test
test: move loading of flexmock and minitest/spec before coverage

The two libraries would otherwise be profiled, which is really
useless.
loaders: RTT defines type handling for 'void', declare it

It is needed to resolve types for operations.
ros,test: update ROS tests
ros: make #import_types_from stricter than the one in Project

While Project#import_types_from has to guess whether its argument
is a file or a typekit (and ignore it if it is a file), there is
no such ambiguity in ROS. Make it stricter by forwarding the call
to using_typekit unconditionally
ros: fix the default superclass in ROS::Spec::Package
gen: fix wrongly placed begin/rescue block

ENOENT is raised by File.read, not by the path resolution code
gen: fix path to the BoostSerialization header
gen,test: refactor the generation-related tests

They get moved into their own subdirectory and the related suite
files got created. Moreover, they get their own SelfTest module
and common header orogen/gen/test
gen,test: add guards to test headers

Otherwise, build breaks because of redefinitions
gen: remove the generate_transports_for_base_type hack

It is not needed anymore in Rock as we have the std typekit,
and was never enabled in the orocos toolchain (e.g. when
using typegen)
gen: set the headers for standard int types to boost/stdint.hpp in normalize_registry

In Rock, it is done by the std typekit. However, it makes orogen
not self-sufficient (does not work anymore without the std typekit),
so add it there as well.
gen: do not auto-export numeric types

This is really not something most people want. In RTT, the users are expecting
RTT to provide them with what they need. In Rock, we have the std typekit for
that.
gen: explicitly include <rtt/TaskContext.hpp> in main.cpp

We are using it, so do not assume that another header is going
to define it for us
gen,test: make sure we can set the -j option to make
gen,test: interpret the TEST_DONT_CLEAN and TEST_KEEP_WC envvars as 'true' only if they are '1'

Otherwise, we can't set them to true globally (for a given shell)
and reset them to false for the time of a single command line, i.e.

  export TEST_DONT_CLEAN=1
  TEST_DONT_CLEAN=0 ruby test/gen/test_build.rb
gen: allow calling #task_context without a block
gen: fix backward compatibility after the change of namespace

Since OroGen::Generation is now equal to OroGen::Gen::RTT_CPP,
the constant resolution skips the constants that are defined
in Gen (!). We therefore have to import them explicitly in
RTT_CPP to keep backward compatibility