build: ipkg-build use fakeroot with PKG_FILE_MODES

build: ipkg-build use fakeroot with PKG_FILE_MODES

The `ipkg-build` script converts a folder into a `opkg` installable
package. Until now it would use root:root for all packages and try to
preserve file modes.

This has the two drawbacks of packages want to add non-root files or add
SUID files, like the `sudo` package does.

To give more flexibility regarding file modes and avoid init script
hacks, a new variable called `PKG_FILE_MODES`. The variable contains a
list of files modes in the format `path:owner:group:mode`.

An example for the `sudo` package below:

```
PKG_FILE_MODES:=\
        /usr/bin/sudo:root:root:4755 \
        /etc/sudoers:root:root:0440
```

The `ipkg-build` now runs within a fakeroot environment to set any mode
and directly store it in the resulting `ipk` package archive.

Both options `-o` and `-g` are no longer required due to the introduction
of the more flexible `-m` options, which takes the `PKG_FILE_MODES` as
input.

Lastly the option `-c` is removed as it's unused within the script.

Signed-off-by: Paul Spooren <mail@aparcar.org>