This bypass had to be re-enabled as some users reported issues,
even after the iconv build fix.

While utf8_to_wide works well, wide_to_utf8 is quite broken
on android, for some reason, and some devices (unrelated from build
configuration).

Before, this lua code led to a crash:

local pcg = PcgRandom(42)
local value = pcg:next()

This was because if you called s32 PcgRandom::range(min, max) with the
minimum and maximum possible values for s32 integers (which the lua
binding code did), u32 PcgRandom::range(bound) got called with 0 as the
bound. The bound however is one above the maximum value, so 0 is a "special"
value to pass to this function. This commit fixes the lua crash by
assigning the RNG's full range to the bound 0, which is also fits to the
"maximum is bound - 1" principle, as (u32)-1 is the maximum value in the
u32 range.

Also misc. minor cleanups

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.