This fixes bug 1551

This was caused by the use the non-threadsafe SharedBuffer in a
threaded context.

When tunnels entirely above ground were avoided, the
missing pseudorandom calls changed the allowed caves.
Now, above ground tunnels are not placed while
still running all previous pseudorandom calls.

Before players "bounced" too high. Now, while still allowing to bounce, higher speed bounces are throttled.

src/server.cpp
src/emerge.cpp

Multiplying by a factor of 1/1000.f (rather than dividing by 1000.f) directly
introduces an error of 1 ULP.  With this patch, an exact comparison of a
floating point literal with the deserialized F1000 form representing it is now
guaranteed to be successful.
In addition, the maxmium and minimum safely representible floating point
numbers are now well-defined as constants.

Before, android_version.h got changed at every new commit. Now, we
only change it with new minetest releases. Analogous to how cmake
does it,  we add an android_version_githash.h file that communicates
the git hash to C++ code.

Also, unify VERS_MAJOR, VERS_MINOR and VERS_PATCH variable
calculation inside the whole makefile.

-> Remove the SendableMediaAnnouncement struct
-> Forge the packet directly in the m_media loop, spare one loop and the construction of a vector
-> Use preincrement to spare iterator copies

Before, our libiconv build was a joke. We first called configure for our own build host system,
then called make, before we executed a Android.mk script we provided as patch. The first "native make"
always failed, and the LIBICONV_LIB file setting in our Makefile didn't match the built one,
resulting in an always-rebuild of iconv.

This commit cleans up this total mess, removes the double-build, and the Android.mk, and properly calls
./configure with the according target platform, and uses a built toolchain.

As we have to deal with the android bug "NDK: Support for prebuild libs with full sonames"
https://code.google.com/p/android/issues/detail?id=55868
as the 2013 patch
https://lists.gnu.org/archive/html/libtool-patches/2013-06/msg00002.html
by Google's David Turner wasn't inside the 2011 libtool, we pass -avoid-version to
libtool.

Thanks to the proper build, wide_to_utf8 works for android now, removing us of the need to disable it.

Thanks @Zeno-

Since 03e0dd33 the calls didn't return an output count
for the recipes.

Also add static identifier as upstream did

always evaluate to true.

This was needed due to the TileDef serialisation changes. Originally it has been planned
to also add utf-8 based chat to 26, but chat changes aren't final yet, so they are done
in one change, after the release, and not two small ones, causing us having to be compliant
to three versions of the packet.

Enable the server to request the client to reconnect.

This can be done with the now extended minetest.request_shutdown([reason], [reconnect]) setting.

Tune and optimise noise parameters