streamclone: clear caches after writing changes into files for visibility Before this patch, streamclone-ed changes are invisible via @filecache properties to in-process procedures before closing transaction (e.g. pretxnclose python hook), if corresponded property is cached before consumev1(). Strictly speaking, caching should occur inside (store) lock for transaction. repo.invalidate() after closing transaction is too late to force @filecache properties to be reloaded from changed files at next access. For visibility of streamclone-ed changes to in-process procedures before closing transaction, this patch clears caches just after writing changes into files. BTW, regardless of changing in this patch, clearing cached properties in consumev1() causes inconsistency, if (1) transaction is started and (2) any @filecache property is changed before consumev1(). This patch also adds the comment to fix this (potential) inconsistency in the future.