Adjustements to compile under Debian Wheezy (32 and 64 bits).
Tested also with Mac OS X 10.8 Mountain Lion.

Summary of changes:

* __OPTIMIZE__ in argp has to be defined to 1 rather than just defined
* getline clashes with libc name, renamed to bow_getline
* added fallback for missing MAXFLOAT
* moved -fnested-functions (needed for Darwin) to a configure check
* regenerated the configure script (due the the above change)