Silence warning: missing AM_PROG_AR on non-POSIX

Automake 1.12 complains: "linking libraries using a non-POSIX archiver
requires 'AM_PROG_AR' in 'configure.ac'". This patch silences this
warning, allowing automake 1.12 to process configure.ac with -Werror
replace fopen with open+fdopen to set more restrictive bits
add check that two challenges get different responses
check for same response in pam module, output debug for the user
bump versions as 2.11 is released
use errstr to communicate with the user
remove -Wno-extra-portability, it breaks on automake before 1.11.2
NEWS for 2.12
copy changes about dependencies from wiki.
bump versions post-release
Verify the otp_length given by the configuration
Avoid out of bound writing at ligne -920,1 +927,1:
strncpy (otp_id, password + skip_bytes, cfg->token_id_length);
Add information about SELinux to README

Because SELinux in enforcing mode will cause yubikey authentication to
fail I'm including some references to discussion around this problem.
The RH bugzilla link also includes a policy snippet which can be used
for this."

This commit should resolve Issue #43.
http://code.google.com/p/yubico-pam/issues/detail?id=43
adding a new line for consistancy with spacing on other headings
Explain what an OTP is
Explain how to generate an OTP.

This wasn't obvious to me and so I suspect others may be confused too.
This commit provides the documentation to close Issue 44, but is NOT
identical to the patch provided on that report.

http://code.google.com/p/yubico-pam/issues/detail?id=44
Attempt to clarify format of mapping files

I didn't realise from the original version that it was a series of
different token IDs - i thought it was different parts of the OTP.
Hopefully this change clarifys whats really going on here.

Part of the patch/doco for Issue 44.
http://code.google.com/p/yubico-pam/issues/detail?id=44
break line so we keep document width consistent
Refer to Github as well as G.Code.

This attempts to help explain where to look for various things (eg
bugs, code, doco).
Correct wording for PPA

Its 'Personal' not 'Private' https://help.launchpad.net/Packaging/PPA
Finish both files with a blank line

Helps to keep all text readable on broken terminals/screens.