Added support to download all dependencies even
if the euid does not have write perms to rootdir.
In this mode we only care if cachedir is writable,
rootdir access is not necessary.
This is really useful to download all binary packages
required by any number of packages as any regular
user to later perform off-line installations, i.e:
```
$ xbps-install -c $PWD/cachedir -yD xbps
...
$ tree cachedir
cachedir/
├── acl-2.2.53_1.x86_64-musl.xbps
├── acl-2.2.53_1.x86_64-musl.xbps.sig
├── attr-2.4.48_1.x86_64-musl.xbps
├── attr-2.4.48_1.x86_64-musl.xbps.sig
├── bzip2-1.0.8_1.x86_64-musl.xbps
├── bzip2-1.0.8_1.x86_64-musl.xbps.sig
├── ca-certificates-20190110_1.noarch.xbps
├── ca-certificates-20190110_1.noarch.xbps.sig
├── libarchive-3.4.1_1.x86_64-musl.xbps
├── libarchive-3.4.1_1.x86_64-musl.xbps.sig
├── libcrypto45-3.0.2_2.x86_64-musl.xbps
├── libcrypto45-3.0.2_2.x86_64-musl.xbps.sig
├── liblz4-1.9.2_1.x86_64-musl.xbps
├── liblz4-1.9.2_1.x86_64-musl.xbps.sig
├── liblzma-5.2.4_2.x86_64-musl.xbps
├── liblzma-5.2.4_2.x86_64-musl.xbps.sig
├── libressl-3.0.2_2.x86_64-musl.xbps
├── libressl-3.0.2_2.x86_64-musl.xbps.sig
├── libssl47-3.0.2_2.x86_64-musl.xbps
├── libssl47-3.0.2_2.x86_64-musl.xbps.sig
├── libtls19-3.0.2_2.x86_64-musl.xbps
├── libtls19-3.0.2_2.x86_64-musl.xbps.sig
├── libxbps-0.57.1_8.x86_64-musl.xbps
├── libxbps-0.57.1_8.x86_64-musl.xbps.sig
├── libzstd-1.4.4_1.x86_64-musl.xbps
├── libzstd-1.4.4_1.x86_64-musl.xbps.sig
├── musl-1.1.24_1.x86_64-musl.xbps
├── musl-1.1.24_1.x86_64-musl.xbps.sig
├── run-parts-4.9.1_1.x86_64-musl.xbps
├── run-parts-4.9.1_1.x86_64-musl.xbps.sig
├── xbps-0.57.1_8.x86_64-musl.xbps
├── xbps-0.57.1_8.x86_64-musl.xbps.sig
├── xbps-triggers-0.113_3.noarch.xbps
├── xbps-triggers-0.113_3.noarch.xbps.sig
├── zlib-1.2.11_3.x86_64-musl.xbps
└── zlib-1.2.11_3.x86_64-musl.xbps.sig
0 directories, 36 files
$
```
Inpired by #213Closes#213
If all packages in transaction are on hold, there's no
need to check for conflicts, shlibs, etc.
This makes `xbps-install -un` work faster on my system:
~0.450ms -> ~0.250ms
There's still room for more improvements :-)
`xbps_transaction_revdeps` will now try to add updates for packages to the
transaction if the dependency is not satisified anymore due to a package
install/update.
`xbps_transaction_prepare` will now check the return value of
`xbps_transaction_revdeps` and repeat the dependency resolution,
until `xbps_transaction_revdeps` returns 0, which means that it didn't
add any new packages to the transaction.
