Edit ccache_def.rst

Re-fill to 70 columns.  Replace non-ascii apostrophes with ASCII ones.
Edit wording slightly.

(cherry picked from commit 482869d393807d02668cf49ce74666d682cf77a6)

https://github.com/krb5/krb5/commit/552c82a0204e8253160b04567b99321978b303d1
Author: Greg Hudson <ghudson@mit.edu>
Committer: Tom Yu <tlyu@mit.edu>
Commit: 552c82a0204e8253160b04567b99321978b303d1
Branch: krb5-1.12
 doc/basic/ccache_def.rst |  162 +++++++++++++++++++++++----------------------
 1 files changed, 83 insertions(+), 79 deletions(-)