* src/stash.c: if we're about to create a ccache with a name identical
to one which we've already created (and haven't since destroyed), try
to make the name unique by appending a "_" to it (mainly for keyrings).
When creating a temporary FILE: ccache, use mkstemp() to generate the
file so that mkstemp patterns don't get used literally. When removing
a ccache, treat EKEYREVOKED when resolving the ccache as a successful
result.