[Bug-readline] How to determine the GPL version at compile and run time ?

[Thomas Schmitt]

Hi,

GPLv2+ licensed libisoburn includes <readline/readline.h> which on
my system says
"GNU General Public License [...] either version 2, or (at your option)
 any later version."

Nevertheless, there is a Debian bug which indicates that meanwhile
the license of their libreadline is GPLv3+.
  https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=749801

libisoburn states its license GPLv2+ in human readable output.
But i understand this is not true anymore if the GPLv3+ version
of libreadline is included and/or linked.
For clarity, i want to adapt that human readable text.

So how do i find out at compile time and especially at run time
what GPL version is granted by libreadline ?

Would it be legal to link a program, that was compiled with
the GPLv3+ header, with a libreadline.so that is under GPLv2+ ?
Does libreadline prevent such a license mix ?
Does libisoburn have to prevent it ?
How much obligation for own effort is legally imposed on users of
libreadline ?


Have a nice day :)

Thomas