Streamline mex build and install process

[blink1073]

Unfortunately, I could not get it working in Windows: http://savannah.gnu.org/bugs/?41833. See my comment below for the gory details.

[coveralls]

Coverage remained the same at 87.24% when pulling 072fe8d on blink1073:master into d1e1988 on arokem:master.

[isbadawi]

Hmm. I'm going to turn off these comments from coveralls -- the info is there in the status box with the Travis status.

[isbadawi]

The comment below says distutils was imported later on purpose. (I'm not really familiar with why though).

[blink1073]

Ah, I see (I guess), I'll move it.

[isbadawi]

Looks good overall. I built the Octave messenger on my mac and it worked fine. The Windows thing I guess is an upstream problem?

I'm OK with merging this after you address the (tiny) comments I made.

I just tried it out and the Octave and MATLAB mex files apparently can coexist in the same directory, and each program will pick up the right one. At this point we could start including pre-built binaries for Octave too.

[blink1073]

Wow, what a nightmare on Windows:
I have been unable to get Java installed on any of the four versions:
3.8.1 MXE:

octave:1> setenv("JAVA_HOME", "C:/Program Files/Java/jdk1.8.0_31/")
octave:2> javaObject
error: unable to find Java Runtime Environment: software\javasoft\java runtime environment::Currentversion

3.6.4 Visual Studio:

octave-3.6.4.exe:1> setenv("JAVA_HOME", "C:/Program Files/java/jdk1.8.0_31")
octave-3.6.4.exe:2> pkg install -forge java
configure: error: in `/c/Users/SILVES~1/AppData/Local/Temp/oct-2/java/src':
configure: error: C compiler cannot create executables
See `config.log' for more details.
the configure script returned the following error: checking for gcc... cc-msvc
checking whether the C compiler works... no
error: called from 'pkg>configure_make' in file C:\Software\Octave-3.6.4\share\o
ctave\3.6.4\m\pkg\pkg.m near line 1373, column 9
error: called from:
error:   C:\Software\Octave-3.6.4\share\octave\3.6.4\m\pkg\pkg.m at line 827, co
lumn 5
error:   C:\Software\Octave-3.6.4\share\octave\3.6.4\m\pkg\pkg.m at line 383, co
lumn 9

3.6.4 Mingw:

octave:1> setenv("JAVA_HOME", "C:/Program Files/java/jdk1.8.0_31/")
octave:2> pkg install -forge java
./configure: line 3257: test: too many arguments
configure: WARNING: this package requires at least Java-1.5
For information about changes from previous versions of the java package, run 'n
ews ("java")'.

Cygwin 3.8.2:

octave:1> setenv("JAVA_HOME", "C:/Program Files/java/jdk1.8.0_31")
octave:2> pkg install -forge java
pkg: unable to find the mkoctfile command, Octave installation is incomplete
error: called from '__gripe_missing_component__' in file /usr/share/octave/3.8.2/m/help/__gripe_missing_component__.m near line 53, column 3
error: called from:
error:   /usr/share/octave/3.8.2/m/pkg/private/install.m at line 199, column 5
error:   /usr/share/octave/3.8.2/m/pkg/pkg.m at line 394, column 9

I tried installing the octave-devel Cygwin package, but it is version 3.8.1 and not compatible, yay!

[blink1073]

I was hoping to phase out Oct2Py, but I don't see that happening until a proper 3.8 release with Java support is available on Windows.

[blink1073]

@isbadawi, ready to roll!