libpng 1.6.40 -> 1.6.42

I've also changed submodule URLs again. git submodule sync is your
friend.

zlib-ng 2.1.4 -> 2.1.6

revert of 0cce80df802490989d1da68336afb2df13343293

Debian buster is now oldoldstable, and there...

zlib-ng 2.1.3 -> 2.1.4

yes, I know it's effectively dead code

just use a null pointer in the vtable instead

this also probably fixed a race bug I introduced in thdat105 while
trying to fix the other race bug

like ds, ddc and daybreak

Fixes #117

this also removes the default seed (5489) that never worked anyway

and some bugfixes!

this won't actually make the -xd option work btw

The compilers aren't smart enough to realize they don't have to emit a
multiplication instructio...

- Immaterial and Missing Power (iamp, 75)
- Super Marisa Land (sml, ...

new test failures (that aren't related to previous ones)
09
Files /tmp/anmtemp/a/result00.anm an...

current results (just as the manpage foretold):
095
Files /tmp/anmtemp/a/front.anm and /tmp/anmt...

doesn't help at all with rebuilding

Turns out #111 wasn't that much of an issue after all.

This is a partial revert of 58be1106561e...

libpng v1.6.38 -> v1.6.40
zlib-ng 2.0.6 -> 2.1.3

broken in fc8057bab87dc102c952458ac7d5c0e6c93ed615

this is more consistent with C++'s stem() function, which is what
thcrap uses for this

because at some point we might need to use this stuff on the wiki

allows th19/pl09.ecl to be recompiled

thanks to SuperChrim for reporting this issue

As it turns out, th19 does not use conventional easy/normal/hard/lunatic
values in its ECL files...

thecl: better support for th185 diffs

resolves #92

fixes #106

now it passes mandoc -mdoc -Tlint

placing newlines after each sentence is necessary for correct...

Most packages don't specify it.

LIBRARY is used for .so on linux

new thanm needs floorf and no one noticed because statically-linked
libpng pulls in libm as a tr...

if(NOT ${x}) checks fail if x is undefined

fixes #44

umask exists for a reason

similar to the one in tar