Use 'banfunc' and 'allowfunc' in .checksrc to specify which functions to
ban or allow to be used. This saves us from having to edit the script
going forward when we want to ban or allow specific functions.
This replaces a set of previous rules and all banned functions are now
checked with the BANNEDFUNC rule.
There is a set of default banned functions, shown by invoking
./checksrc.
Also, -a and -b options are added to specify allowed or banned functions
on the command line.
Closes#15835
It would previously wrongly also catch function calls to function names
ending with 'return'
Amended test1185.
Reported-by: Stefan Eissing
Closes#15764
Move checksrc.pl, firefox-db2pem.sh and mk-ca-bundle.pl since they don't
particularly belong in lib/
Also created an EXTRA_DIST= in scripts/Makefile.am instead of specifying
those files in the root Makefile.am
Closes#8625