Suspected "use after free" in nsMsgLineStreamBuffer::ReadNextLine() leading to crash since object may be destroyed while still in use on another thread.
Tag #1273
Also factors out some common code into nsMSgDBFolder::Delete(), and makes a couple of incidental changes to try and clarify the responsibilies of nsIMsgPluggableStore::DeleteFolder().
Tag #1273
* Part 1: make conversion CTORs explicit.
Minor tweaks to conform with new(ish) static analysis rule which flags up implicit single-argument conversion constructors.
* Part 2: fix a couple of double-mRefCnt declaration errors.
* Part 3: Fix unsafe use of NS_ConvertASCIItoUTF16().
Tag #1273
