setup with experimental libsolv-based dependency solving

[Jon Turney]

On 25/10/2017 20:18, Jon Turney wrote:
> 
> This has a lot of internal changes, so could use some wider testing. 
> Please test.
> 
>  Â  https://cygwin.com/setup/setup-2.882-41-g4cbfa1.x86.exe
>  Â  https://cygwin.com/setup/setup-2.882-41-g4cbfa1.x86_64.exe

I've replaced these with:

    https://cygwin.com/setup/setup-2.882-49-gcc8b05.x86.exe
    https://cygwin.com/setup/setup-2.882-49-gcc8b05.x86_64.dbg

Changes compared to 2.882-41-g4cbfa1:

- Fix installed.db getting emptied if installing from a local directory, 
which didn't contain a setup.ini
- Read epochal version numbers correctly from installed.db
- Remove the ability to install package files from a local directory 
which didn't contain a setup.ini
- Updated build instructions