For proper cross-build support, the subpackage arch needs to
be known before invoking the split function. This implements
a way to do that. This also changes to write the actual subpkg
arch to .PKGINFO - apk index --rewrite-arch still overwrites
index to have machine arch for noarch packages.

apkbuild-cpan: fixed error "Experimental keys on scalar is now forbidden" due to perl upgrade to 5.24 version

fixes to pick correct subpackage name when "pkg:split:arch" syntax
is used.

it's annoying flickering, and results the title being unset for
the time when last split is executed and packages are created.

This is in preparation to support subpackages="pkg:split:arch"
syntax, and just makes the current code ignore anything after
the second colon if it exists. This allows to use the new syntax
in aports git without running experimental abuild on the official
builders.

we probably will not be able to run the scripts as it can
be incompatible system type

Fix filename_from_uri call
Ensure remote sources are fetched
Include remote sources in source package
Include pre/post scripts
Include trigger scripts

The previous deletion of file did not work properly at all. Fix
this instead to rename the file, so we keep the previous download.
This allows builders to redownload upstream file if the checksum
has been changed in aports.

this allows blacklisting architectures instead of just
whitelisting them. useful when more architectures comeabout.

unzip(1) is verbose by default since we don't run tar(1) in verbose mode
we should run unzip with -q for consistency.

"apk del" now returns error if the package name does not exist.
Thus when cross compiling, always install the virtual
.makedepends-$pkgname name for chroot also since undeps() will
try to uninstall it always.

If $sdir is not defined find writes an error message to stderr. For
example when running:

	newapkbuild -n foo -a foo

You will see a find error message because no source url was provided.
This commit silences any find error message. An alternative solution
would be to not invoke find unless $sdir is set.

fix check that all subpackages exists, not only main package

splice is a linux thing.

Few days ago some user on IRC pointed out that the current error message:

    abuild-apk: Not a member of group abuild

is confusing. He was trying to build a package using abuild -r and
didn't know what this message means.

fixes #5408

some packages don't have patches. We should not error if builddir is not
set in this case.

the _builddir should never been used bu abuild due to the _ prefix.

the _ prefix is reserved for APKBUILD. This is to avoid use variable
names in APKBUILD that may clash with abuilds internal vars