Don't register HUP signal handler on Windows
Don't register HUP signal handler on Windows

Don't register HUP signal handler on Windows.

Fixes:

```
$ bin/riemann etc/riemann.config
INFO [2013-06-20 09:08:13,593] main - riemann.bin - PID 277056

ERROR [2013-06-20 09:08:13,594] main - riemann.bin - Couldn't start
java.lang.IllegalArgumentException: Unknown signal: HUP
        at sun.misc.Signal.<init>(Unknown Source)
        at riemann.bin$handle_signals.invoke(bin.clj:36)
        at riemann.bin$_main.doInvoke(bin.clj:58)
        at clojure.lang.RestFn.applyTo(RestFn.java:137)
        at riemann.bin.main(Unknown Source)
```
vixns/riemann,rekhajoshm/riemann,cswaroop/riemann,lispmeister/riemann,hugoduncan/riemann,pyr/riemann,bwilber/riemann,bmhatfield/riemann,patrickod/riemann,VideoAmp/riemann-1,udoprog/riemann,riemann/riemann,mfournier/riemann,vixns/riemann,Anvil/riemann,mbuczko/riemann,nelhage/riemann,cswaroop/riemann,yeller/riemann,forter/riemann,robashton/riemann,stanislas/riemann,robashton/riemann,eric/riemann,mfournier/riemann,moonranger/riemann,irudyak/riemann,nberger/riemann,nberger/riemann,bowlofstew/riemann,alq666/riemann,tzach/riemann,mirwan/riemann,nelhage/riemann,topecz/riemann,vincentbernat/riemann,lispmeister/riemann,rhysr/riemann,pharaujo/riemann,aphyr/riemann,abailly/riemann,timbuchwaldt/riemann,algernon/riemann,forter/riemann,moonranger/riemann,ClodoCorp/riemann,LubyRuffy/riemann,tzach/riemann,twosigma/riemann,udoprog/riemann,mbuczko/riemann,stanislas/riemann,forter/riemann,pradeepchhetri/riemann,patrickod/riemann,vincentbernat/riemann,irudyak/riemann,jamtur01/riemann,ClodoCorp/riemann,stanislas/riemann,DasAllFolks/riemann,bmhatfield/riemann,shokunin/riemann,bwilber/riemann,VideoAmp/riemann-1,rekhajoshm/riemann,shokunin/riemann,rhysr/riemann,fullcontact/riemann,twosigma/riemann,DasAllFolks/riemann,riemann/riemann,mfournier/riemann,bg451/riemann,micrub/riemann,cswaroop/riemann,mirwan/riemann,shokunin/riemann,counsyl/riemann,twosigma/riemann,timbuchwaldt/riemann,patrox/riemann,LubyRuffy/riemann,bfritz/riemann,fullcontact/riemann,jamtur01/riemann,patrickod/riemann,aphyr/riemann,abailly/riemann,bowlofstew/riemann,topecz/riemann,zamaterian/riemann,bg451/riemann,yeller/riemann,patrox/riemann,patrox/riemann,counsyl/riemann,pharaujo/riemann,zamaterian/riemann,micrub/riemann,mirwan/riemann,AkihiroSuda/riemann,algernon/riemann,topecz/riemann,tzach/riemann,rekhajoshm/riemann,Anvil/riemann,AkihiroSuda/riemann,hugoduncan/riemann,joerayme/riemann,fullcontact/riemann,nelhage/riemann,eric/riemann,pradeepchhetri/riemann,ClodoCorp/riemann,lispmeister/riemann,bfritz/riemann,micrub/riemann,algernon/riemann,joerayme/riemann,rhysr/riemann,udoprog/riemann,jeanpralo/riemann,yeller/riemann,jeanpralo/riemann,alq666/riemann,pyr/riemann,hugoduncan/riemann