Patch double free or corruption (fasttop) when stopping inadyn.

Glibc complained about the following when rebooting with inadyn running
or when stopping inadyn:

~ # killall inadyn
*** Error in `/sbin/inadyn': double free or corruption (fasttop): 0x0003e708 ***

Turns out to be caused by a careless free() in atexit() handler.  This
patch makes sure to double check all pointers before freeing them, and
restoring pointers to NULL when handling a SIGHUP.

Signed-off-by: Joachim Nilsson <troglobit@gmail.com>
Fix problem with include order for error.h when cross-compiling ...

Signed-off-by: Joachim Nilsson <troglobit@gmail.com>
Use strlcpy() for first write to temp. buffer, not strlcat().

Signed-off-by: Joachim Nilsson <troglobit@gmail.com>
Improve debug logging for Base-64 user:pass encoding.

Signed-off-by: Joachim Nilsson <troglobit@gmail.com>