Fix Linux build problems

[ngaro]

• Adds 2 missing headers needed for compiling
• Removes a definition already defined earlier (not necessary)
• Fixes problems with incorrect gcc options
• Automatically download and build the correct version of openssl
• Add possibility for cleaning the build environment

[Ri1a]

I changed the lines you committed, but I still got one error:

"gcc: error: ../heartleech/heartleech.c: No such file or directory"

I also reinstalled it and modified the path, but this didn't help. Did I do sth wrong?

[ngaro]

I tried it again here, works fine. You must be compiling it wrong. I can compile my rep like this: git clone [email protected]:ngaro/heartleech.git && cd heartleech && make