* fix hashbangs
* remove strict requirements of python2 in build system

Resolves:
https://fedorahosted.org/sssd/ticket/2017

Reviewed-by: Petr Viktorin <pviktori@redhat.com>
(cherry picked from commit e8058322725ba050014777ee2484f7e833ab1e3a)

https://fedorahosted.org/sssd/ticket/2017
(cherry picked from commit 341a00311680a440d7f979f06c34c70d86c9367a)

The configure script failed with python3

checking for python... /usr/bin/python
checking for python version... 3.3
checking for python platform... linux
checking for python script directory... ${prefix}/lib/python3.3/site-packages
checking for python extension module directory... ${exec_prefix}/lib64/python3.3/site-packages
checking for headers required to compile python extensions...   File "<string>", line 1
    import sys; print sys.prefix
                        ^
SyntaxError: invalid syntax
  File "<string>", line 1
    import sys; print sys.exec_prefix
                        ^
SyntaxError: invalid syntax
not found
configure: error: Could not find python headers

Reviewed-by: Jakub Hrozek <jhrozek@redhat.com>
Reviewed-by: Pavel Reichl <preichl@redhat.com>

AC_MSG_RESULT was not used everywhere after AC_MSG_CHECKING.
Therefore two lines from configure output was mixed in some cases.

Detect directory with python libraries and add this
directory to the list of directories to be searched for linker.

Several parts of the HBAC python bindings did not work with old Python
versions, such as the one shipped in RHEL5.

The changes include:
* a compatibility wrapper around python set object
* PyModule_AddIntMacro compat macro
* Py_ssize_t compat definition
* Do not use PyUnicode_FromFormat
* several function prototypes and structures used to have "char
  arguments where they have "const char *" in recent versions.
  This caused compilation warnings this patch mitigates by using
  the discard_const hack on python 2.4

Also update BUILD.txt