build, i18n: improve Intl build, add "--with-intl"

The two main goals of this change are:
 - To make it easier to build the Intl option using ICU (particularly,
   using a newer ICU than v8/Chromium's version)
 - To enable a much smaller ICU build with only English support The goal
   here is to get node.js binaries built this way by default so that the
   Intl API can be used. Additional data can be added at execution time
   (see Readme and wiki)

More details are at https://github.com/joyent/node/pull/7719

In particular, this change adds the "--with-intl=" configure option to
provide more ways of building "Intl":
 - "full-icu" picks up an ICU from deps/icu
 - "small-icu" is similar, but builds only English
 - "system-icu" uses pkg-config to find an installed ICU
 - "none" does nothing (no Intl)

For Windows builds, the "full-icu" or "small-icu" options are added to
vcbuild.bat.

Note that the existing "--with-icu-path" option is not removed from
configure, but may not be used alongside the new option....