Implement switch_to for ccapiv3

krb5_stdccv3_switch_to() calls cc_ccache_set_default().
krb5_stdccv3_resolve() checks for NULL or empty residual and calls
cc_context_get_default_ccache_name() in those cases.

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

(cherry picked from commit 2648a94ea1cf3dec91186dfec59b75de9dac793d)

https://github.com/krb5/krb5/commit/02ea50fe1b211841399eed993eac99a96371582d
Author: Kevin Wasserman <kevin.wasserman@painless-security.com>
Committer: Tom Yu <tlyu@mit.edu>
Commit: 02ea50fe1b211841399eed993eac99a96371582d
Branch: krb5-1.10
 src/lib/krb5/ccache/ccapi/stdcc.c |   25 +++++++++++++++++++++++++
 src/lib/krb5/ccache/ccapi/stdcc.h |    2 ++
 2 files changed, 27 insertions(+), 0 deletions(-)