* 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
This only applies to non-literal+ appends. Bad response typically occurs when {size} parameter of append command is larger than server can accept. This prevents TB from sending megabytes of data to a server that has already rejected it.
Tag #1273
This is because it was only used in response to a CAPABILITY imap request. However, often CAPABILITY response occurs without a request so TB sees no need to do a request. Fix by moving the usage of use_literal_plus to where LITERAL+ capability is actually used.
Tag #1273
