abuild, abuild-keygen: drop echo -n as well

See merge request !4

tests: fix newapkbuild tests

See merge request !2

* Do not use the -n option for newapkbuild_simple_test: since commit
  a68354eb, this option is not allowed
  when providing PKGNAME[-PKGVER] (i.e. not SRCURL) as the final
  argument.
* Use newapkbuild from the working tree, not whatever is in $PATH.

POSIX me harder

See merge request !3

According to POSIX, the "command -v" form of command(1) accepts only a
single argument (command_name). Some shells will check additional
arguments, but not dash.

This was causing build issues when sharing ~/abuild between arches.