modelbuilder: avoid infinitive recursion in case of module importation loops

Signed-off-by: Jean Privat <jean@pryen.org>
nitx: only depends on modelize_property instead of the full frontend

~~~
$ time ../bin/nitx nitg.nit :q # before
real	0m2.775s
user	0m2.660s
sys	0m0.112s
$ time ./nitx nitg.nit :q # after
real	0m1.436s
user	0m1.328s
sys	0m0.104s
~~~

Signed-off-by: Jean Privat <jean@pryen.org>
Merge branch 'fast_nitx'
modelbuilder: display error in case of dependency loop

Signed-off-by: Jean Privat <jean@pryen.org>
tests: error_req_loop*

Signed-off-by: Jean Privat <jean@pryen.org>
Merge branch 'error_req_loop'
Merge remote-tracking branch 'alexis/android-platform'

Add support to compile for Android with nitg. When the "android" module
is imported, nitg will generate an APK instead of a binary,

The option --no-stacktrace must be used for Android. This is why we
expect the test to fail.

The generate applications are not usable (as of yet) since they are only
console

To do next:

* Solve the --no-stacktrace problem.
* Implement mnit for Android
share/png: intro the libpng base code for the Android platform

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>
share/png: configure the png library for android

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>
share/png: add Android specific makefiles to the png library

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>
lib: intro the android implementation of mnit

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>
lib: import the android module from mnit_android

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>
nitg/android: add a deeper folder to generated project

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>
nitg/android: compile with the png lib

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>
nitg/android: load assets on the APK

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>
example: update mnit examples with android version

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>