utils: fix error on remote command call

The number of arguments was not checked on the call of a remote command
template: fix missing INCLUDE_DIRS for extensions
devs: fix Dynamics::init() with negative Time

We add a check in the vle::devs::Simulation::init(...) function to
ensure that only positive Time are authorized. (Closes #120)
vle: add CXX and CC flags for Clang

By default, only GNU GCC and G++ have -Wall and -Wextra option. We add
option for Clang too.
devs: improve the positive and negative infinity test

From the C99, POSIX.1, for the isinf() function: "the standards merely
say that the return value is  nonzero if and only if the argument has an
infinite value". So, we update the check to test if isinf() > 0 or
isinf() < 0 insteaf of == 1 or == -1.
utils: remove unused variables
test: hide declaration of get_temporary_path

The get_temporary_path() function only necessary when Boost < 1.45 is
installed (Closes #107).
devs: remove unused variable

The FinishView declares an unused variable m_last. We remove it.
vle: use class instead of struct with Pimpl

For the PIMPL idiom, in header file, we use "class Pimpl" and in the
sources files, we use struct Pimpl. We homogenize declaration.