Can't modify constant item in postincrement line 727, near "i++"

...and updated test902 as explicit HELO response is no longer required.

...in both the IMAP LOGIN and POP3 PASS handlers introduced in commit
187ac693 and 84ad1569 respectively.

...which was accidentally introduced in commit 4d6ef629.

URL: http://curl.haxx.se/bug/view.cgi?id=1279
Suggested-by: Jerry Krinock

Commit 32352ed6 introduced various DNS options, however, these
would cause curl to exit with CURLE_NOT_BUILT_IN when c-ares wasn't
being used as the backend resolver even if the options weren't set
by the user.

Additionally corrected some minor coding style errors from the same
commit.

URL: http://curl.haxx.se/bug/view.cgi?id=1278
Reported-by: Gorilla Maguila

(Passed on to c-ares.)

Allows something like this:

curl --dns-interface sta8 --dns-ipv4-addr 8.8.1.111 --interface sta8 \
--localaddr 8.8.1.111 --dns-servers 8.8.8.1 www.google.com

Signed-off-by: Ben Greear <greearb@candelatech.com>

... and a few more cleanups/clarifications

Global symbol "$mailbox" requires explicit package name

...as this will be required for IMAP CLOSE and EXPUNGE commands as well
as the POP3 RSET command.

Solaris with the SunStudio Compiler is reportedly missing this define,
but as we're using it without any good reason on all the places it was
used I've now instead switched to just use sensible buffer sizes that
fit a 32 bit decimal number. Which also happens to be smaller than the
common NI_MAXSERV value which is 32 on most machines.

Bug: http://curl.haxx.se/bug/view.cgi?id=1277
Reported-by: D.Flinkmann

... instead of HTTP/2.0 to work fine with the nghttpx proxy/server.

warning: comparison between signed and unsigned integer expressions

Don't wait for the next callback call (usually 1 second) before
continuing with protocol specific connection initialization.