don't cache .parrot_current_git_describe

[coke]

When configuring parrot, the value for "git-describe" is taken from the cache file if it is present.

Here's a not-uncommon workflow that breaks in this case:

• realclean
• build
• git pull
• configure # XXX This does not update the sha1-describe.
• build

Unless there's a super compelling reason to cache this file, the value shouldn't even be stored on disk - it should go into the config hash and be calculated every time you run configure.

(similar arguments may cover other newly generated .parrot files.)

[coke]

(fix formatting in desc.)

[jkeenan]

This would probably apply mainly to:

.parrot_current_git_describe
.parrot_current_rev
.parrot_current_sha1

(Although I believe .parrot_current_rev is needed mainly for backwards-compatibility reasons.)

dukeleto,

As these config steps were mainly your work, can you comment?

Thank you very much.

kid51