cURL: implement new functionality with cleanup and fixes

cURL: implement new functionality with cleanup and fixes

remove obsolete configuration settings
  --disable-thread
  --enable-nonblocking
  --without-krb4
remove SSPI support
  only supported on windows
correct --with/without-ca-path handling
  only supported with OpenSSL and PolarSSL
correct LDAP/LDAPS protocol
  add dependency libopenldap
added SCP/SFTP protocol
  default "No"
  depends on libssh2
added IDN support
  default "No"
  depends on libidn
added SMB protocol (new in 7.40)
  default "No"
  require 'cryptographic authentication' and either 'GnuTLS' or 'OpenSSL' selected
added Unix sockets support (new in 7.40)
  default "No"
added error verbose messages
  default "No"
changes to Makefile
  Increase PKG_RELEASE
  PKG_CONFIG_DEPENDS and CONFIGURE_ARGS
    extended for new functionality
    use "autoconf_bool" for all --enable/--disable options
    restructure for easier reading
changes to Config.in
  extended for new functionality
  implement dependencies
  restructure and grouping for easier reading
build tested on XUbuntu 14.10 x86 for x86 (generic) and ar71xx (WNDR3800)

Signed-off-by: Christian Schoenebeck <christian.schoenebeck@gmail.com>
git-svn-id: svn://svn.openwrt.org/openwrt/trunk@44243 3c298f89-4303-0410-b956-a3cf2f4a3e73