don't have prototypes. They didn't serve any useful purpose here, anyway.

Changed checkprefix() to use it and those instances of strnequal() that
compare host names or other protocol strings that are defined to be
independent of case in the C locale.  This should fix a few more
Turkish locale problems.

run-time relocations.

dereferenced here, if the app passes in a funny combo. Detected by coverity.com

by coverity.com

GTLS.

--disable-proxy mode.
Removed some unnecessary prototypes.

CURLOPT_PROXYUSERPWD

  make CURLOPT_PROXYUSERPWD sort of deprecated. The primary motive for adding
  these new options is that they have no problems with the colon separator
  that the CURLOPT_PROXYUSERPWD option does.

used in strequal.c so now all test cases run fine for me again.

are consecutive and with a 0x20 "distance" to the uppercase letter), since we do
support EBCDIC as well. Thus I replaced the macro with a (larger) switch case.

I better change the function name...

  (http://curl.haxx.se/bug/view.cgi?id=2154627) which pointed out that libcurl
  uses strcasecmp() in multiple places where it causes failures when the
  Turkish locale is used. This is because 'i' and 'I' isn't the same letter so
  strcasecmp() on those letters are different in Turkish than in English (or
  just about all other languages). I thus introduced a totally new internal
  function in libcurl (called Curl_ascii_equal) for doing case insentive
  comparisons for english-(ascii?) style strings that thus will make "file"
  and "FILE" match even if the Turkish locale is selected.

  (http://curl.haxx.se/bug/view.cgi?id=2155496) pointing out an error case
  without a proper human-readable error message. When a read callback returns
  a too large value (like when trying to return a negative number) it would
  trigger and the generic error message then makes the proplem slightly
  different to track down. I've added an error message for this now.