kvs: key of a...b confuses kvs

[garlick]

Consecutive path separators in the middle of a key are not handled properly.

$ flux kvs put a..b=42
$ flux kvs get a
$ flux kvs get a.
flux-kvs: a.: Is a directory
$ flux kvs get a..
flux-kvs: a..: No such file or directory
$ flux kvs get a..b
42
$ flux kvs ls -RF a
a:
.

a.:
b
$ flux kvs ls -RF
.:
a.          foo.        resource.

a:
.

a.:
b

[snip]

[garlick]

Keys should undergo "normalization" in the KVS service before they are passed to any internal functions. This would involve transforming multiple consecutive path separators to a single one.

Since we have no concept of "current working directory", leading path separators can be stripped.

We need some rules for handling trailing path separators, as discussed in #1173.

Test cases are needed.