computed sieve.c
[sieve] sieve.y: verify :flags parameter is a valid list of flags
[sieve] sieve.y: free_ftags(): free flags stringlist
[sieve] sieve.y: support for space-separated flags within a string

Effectively change "flag1 flag2" to ["flag1", "flag2"]
Revert "computed sieve.c"

This reverts commit b9df8a67e13f1e1712da832c04ece05c059cca36.