Make python-igraph easy_installable at least on Linux and Mac OS X

[gaborcsardi]

From @gaborcsardi on May 4, 2013 18:42

easy_install python-igraph works only when the C core library has already been compiled and installed. Most users do not bother to read the documentation and do not realize that the C core has to be compiled beforehand.

The setup script should do at least the following before trying to build igraph:

• Check whether the library and the include files are already there.
• If they are not, the user should be asked whether he wants to download and compile it or whether he wants to specify an alternate location where these files are to be found.

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Imported from Launchpad using lp2gh.

• date created: 2011-01-30T18:34:28Z
• owner: ntamas
• assignee: ntamas
• the launchpad url was https://bugs.launchpad.net/bugs/710276

Copied from original issue: igraph/igraph#83