Add another stage 'check' between 'build' and 'install'. It is be enabled using the
variable XBPS_CHECK_PKGS=yes and disabled if unset, set to "0" or "no" in your
local etc/conf.
A new xbps-src option `-q` for `quick` will disable XBPS_CHECK_PKGS by overriding it to 0.
If enabled, `common/xbps-src/shutils/xbps-src-docheck.sh` checks for an existing
`do_check()` function in the package's template and, if it exists, calls it.
A new template variable `checkdepends` may be present and list packages required
to run the `do_check()` function. Example: `checkdepends="bc unittest-cpp"`.
