Use file mapping to marshall message data

GlobalAlloc() is no longer supported for this purpose.
Also split out leash message marshalling code into a separate function
acquire_tkt_send_message_leash and improve string copy safety.

Signed-off-by: Kevin Wasserman <kevin.wasserman@painless-security.com>

https://github.com/krb5/krb5/commit/e2ad5d74adbf3edc8a7026cad8283c0077377e81
Author: Kevin Wasserman <kevin.wasserman@painless-security.com>
Committer: Ben Kaduk <kaduk@mit.edu>
Commit: e2ad5d74adbf3edc8a7026cad8283c0077377e81
Branch: master
 src/windows/leash/LeashView.cpp |   15 +++-
 src/windows/leashdll/lshfunc.c  |  160 +++++++++++++++++++++++++++-----------
 2 files changed, 126 insertions(+), 49 deletions(-)