system emails: TO does not include display name; BCC processed as TO

there are a couple issues with how emails are constructed by the system in 4.1.5. i'm specifically seeing this with contrib receipts, but it's caused by the main mail send method, so it probably impacts a lot of areas.

issue 1:
the TO value passed to the mailing engine is the email only, instead of the display name + email in RFC standard format. issue is with CRM_Utils_Mail::send() around line 148 – even though we've earlier constructed the $headers['To'] using the RFC standard, we set that $to value here to just the email. it should be set to the header value.

issue 2:
same method, around line 155 – we are retrieving the BCC and appending it as a TO value. that's not necessary. in my testing, if we just leave it as part of the headers array, it is sent as a true BCC. simply removing the two lines (where the bcc is added as a to value, and then unset) fixes things.

the second issue, IMHO, is really important. people use blind carbon copies so that the recipient is not aware that a copy was sent. the function is premised on privacy. the fact that we expose the bcc as just another TO recipient is very misleading and problematic.