pgsql: Fix unportable disregard of alignment requirements in RADIUScod

Fix unportable disregard of alignment requirements in RADIUS code.

The compiler is entitled to store a char[] local variable with no
particular alignment requirement.  Our RADIUS code cavalierly took such
a local variable and cast its address to a struct type that does have
alignment requirements.  On an alignment-picky machine this would lead
to bus errors.  To fix, declare the local variable honestly, and then
cast its address to char * for use in the I/O calls.

Given the lack of field complaints, there must be very few if any
people affected; but nonetheless this is a clear portability issue,
so back-patch to all supported branches.

Noted while looking at a Coverity complaint in the same code.

Branch
------
REL9_2_STABLE

Details
-------
http://git.postgresql.org/pg/commitdiff/5fe937f38b493f7c94c4ef8b0940e034afbd78a6

Modified Files
--------------
src/backend/libpq/auth.c | 21 ++++++++++++---------
1 file changed, 12 insertions(+), 9 deletions(-)