Linux autotools patch

[AmatCoder]

Hi to all!

I wrote one patch to fix building with autotools on Linux.
It is in a weird state right now and most probably it would require more improvements.
These are the minimum changes to bring it to a state where it can be used to compile PCem.

Changes are:

• allegro.m4 file is added and configure.ac is modified to find it.
• Symlinks are removed. Now they are regular files.
• Scripts rebuilt

Regards.

[AmatCoder]

Here another patch to fix segfault when there are no roms presents.

[SarahWalker]

Segfault fix patch committed at rev 653.

[SarahWalker]

Autotools patch committed at rev 654.