testing: added SafeBuffer
testing: added SafeBuffer

This is just a thread safe version of bytes.Buffer. Actually, it wraps
a bytes.Buffer with a mutex.

tsuru/tsuru,cgvarela/tsuru,guilhermebr/tsuru,mderaldo/tsuru,jblancett/tsuru,RichardKnop/tsuru,mderaldo/tsuru,cezarsa/tsuru,kgrvamsi/tsuru,Endika/tsuru,ArxdSilva/tsuru,tsuru/tsuru,cezarsa/tsuru,gciotta/tsuru,ggarnier/tsuru,4eek/tsuru,tsuru/tsuru,hugoantunes/tsuru,firebitsbr/tsuru,ArxdSilva/tsuru,mderaldo/tsuru,firebitsbr/tsuru,kgrvamsi/tsuru,tuxmonteiro/tsuru,ggarnier/tsuru,RichardKnop/tsuru,RichardKnop/tsuru,hugoantunes/tsuru,ArxdSilva/tsuru,ggarnier/tsuru,jblancett/tsuru,guilhermebr/tsuru,tsuru/tsuru,guilhermebr/tsuru,gwmoura/tsuru,gwmoura/tsuru,4eek/tsuru,Endika/tsuru,hcxiong/tsuru,4eek/tsuru,gciotta/tsuru,ArxdSilva/tsuru,hcxiong/tsuru,firebitsbr/tsuru,jblancett/tsuru,cezarsa/tsuru,cgvarela/tsuru,tuxmonteiro/tsuru,hcxiong/tsuru,gciotta/tsuru,guilhermebr/tsuru,tuxmonteiro/tsuru,Endika/tsuru,ggarnier/tsuru,cezarsa/tsuru,kgrvamsi/tsuru,gwmoura/tsuru,cgvarela/tsuru