Description:
------------
Tests for SHA-2 family functions in crypt() from -lcrypt are broken:

strcpy(&answer[29],"$6$$QMXjqd7rHQZPQ1yHsXkQqC1FBzDiVfTHXL.LaeDAeVV.IzMaV9VU4MQ8
kPuZa2SOP1A0RPm772EaFYjpEJtdu.");

in SHA-512 test will surely not fit into char answer[80]...  and because of that 
salt (on the stack) is overwriten, same problem with SHA-256.  But even if you 
increase the buffer, the code there is just plain wrong and could never function 
correctly.

Looks like this code was not properly tested since there are probably too few 
platforms where you can satisfy all needed crypt functions (extended DES and 
Blowfish) and therefore internal crypt implementation is always used.

Attached patch corrects that.

If I have a more time I'll rework this whole code, to just use internal 
reimplementations for functions not provided by system library.

Expected result:
----------------
checking for SHA512 crypt... yes
checking for SHA256 crypt... yes

Actual result:
--------------
checking for SHA512 crypt... no
checking for SHA256 crypt... no