cygwin: remove unused variable
build: -Wno-dollar-in-identifier-extension is clang only

Add a compiler check because turning on the option unconditionally
breaks the build when CC=gcc.

This should also fix the build on versions of OS X that predate Apple's
switch to clang (10.6 and older.)
2013.04.12, Version 0.10.4 (Stable)

Changes since version 0.10.3:

* include: update uv_backend_fd() documentation (Ben Noordhuis)

* unix: include uv.h in src/version.c (Ben Noordhuis)

* unix: don't write more than IOV_MAX iovecs (Fedor Indutny)

* mingw-w64: don't call _set_invalid_parameter_handler (Nils Maier)

* build: gyp disable thin archives (Timothy J. Fontaine)

* sunos: re-export entire library when static (Timothy J. Fontaine)

* unix: dtrace probes for tick-start and tick-stop (Timothy J. Fontaine)

* windows: fix memory leak in fs__sendfile (Shannen Saez)

* windows: remove double initialization in uv_tty_init (Shannen Saez)

* build: fix dtrace-enabled out of tree build (Ben Noordhuis)

* build: squelch -Wdollar-in-identifier-extension warnings (Ben
  Noordhuis)

* inet: snprintf returns int, not size_t (Brian White)

* win: refactor uv_cpu_info (Bert Belder)

* build: add support for Visual Studio 2012 (Nicholas Vavilov)

* build: -Wno-dollar-in-identifier-extension is clang only (Ben
  Noordhuis)
Now working on v0.10.5
Merge branch 'v0.10'