Support for AOSP su (without -c argument)

[vgavro]

AOSP "su" version never had "-c" flag option, like I see from sources. I tried not to break compatibility with previous tsu version, while trying to determine AOSP su by --help, or (in case for older android versions) you may explicitly set it like SU_AOSP=1 sudo id

[vgavro]

related to https://github.com/cswl/tsu/issues/72

[vgavro]

Besides adding support for aosp su binaries - there are plenty fixes I found which I had to fix, sorry for this LARGE pull request... I hope it could be merged to upstream anyway...

• ./scripts/tadb was outdated and not functional - replaced it with ./scripts/adb-termux; it will be good if ./scripts/adb-termux-helper will be included in termux "tsu" package.. @Grimler91
• setting empty LD_PRELOAD breaks my system with linking errors - so setting LD_PRELOAD only if it was already set before;
• tsu added ONLY termux path but no android system path at all, even with -p/-a options - obviously this was error on adding new LD_LIBRARY_PATH logic (PATH was empty if LD_LIBRARY_PATH was set - or this was really intentional?) related to #63
• -a option is just unnecessary - it's set by default anyway (if prepend was not requested)
• added /vendor/bin to extra syspath
• added extra check if /sbin/su exists - not to get error in stderr that binary not exists on trying to check it version
• merged #75
• hope haven't broke anything besides

TODO/NOTES:

• I don't like ~/.suroot home name - maybe it should be named ~/.tsu for consistency, maybe even ~/.termux/tsu. Better if we have less unique names that you should remember...
• I don't see why ~/.termux/tsu/.tmp should be prepended with .
• calling su -c PATH=x env VARIABLE=y CMD - like I understand - made for cases when we need to find "env" binary? This fails on my aosp su with error PATH=x executable not found (so I changed it only for aosp) - but I guess PATH=x should be moved after env for other su versions.
• Please - review ./scripts/adb-termux-helper variables - I guess most of them are useless.

My proposition - to release next major version (9.0) and rename .suroot to .tsu. Thanks for you time!