Revamp Makefiles to better conform to common packaging guidelines

* Change/create Makefile variables to more standard names
  * `$(PREFIX)` -> `$(prefix)`, `$(PREFIX)/bin` -> `$(bindir)`, etc.
  * Also create new `$(build_prefix)` and `$(build_bindir)` makevars to abstract away "build time" tree layout from "install time" tree layout
  * Because we can now flexibly set the build layout, a fair amount of windows-specific checks and moves can be removed
  	* we just set `$(build_libdir) = $(build_bindir)`, and this transparently makes its way through configure scripts and Makefiles

* Relocates binaries' RPATH entries on install
  * This is necessary when build-time tree layout != install-time tree layout
  * Better than changing build-time tree layout, as that requires a reconfiguration of all deps
  * Only done if the relative path from `julia` to `libjulia` changes between compilation and installation

* Adds tool to replace strings in binaries (`contrib/stringpatch.c`)
  * Used to overwrite `image_file` hardcoded in julia binary in `ui/repl.c` [here]().
  * Source modified to include ample extra space so if the new path is longer, we don't overwrite anything important
  * This modification is only done if the relative path from `julia` to `sys.ji` changes between compilation and installation
    * You can prevent this from happening if you know apriori what install-time tree layout you want, by setting `build_libdir` and friends.

* Passes `make testall` in both the build directory (e.g. after a `make`) and in a foreign installed directory (e.g. after a `make install prefix=/usr/local libdir=/usr/local/lib64 DESTDIR=/tmp/jdst`) on OSX, Ubuntu and Windows cross-compile.

* Changes `$(libdir)` on windows to be equal to `$(bindir)` instead of equal to just `bin`.  This gets rid of some special-cases we've needed in the past.
Fix git rebase artifact
Add maxlen parameter to stringpatch to avoid corrupting binaries with extremely long paths
Remove windows special-casing of bindir/libdir
Quash compiler warnings about printing maxlen
Add makefile rule to automatically rebuild stringpatch
Install libgcc_s*.dll and friends to $(build_bindir), not $(build_libdir)
Purge sys.{dll,so,dylib} in make dist