make retry middleware changes backwards compatible
make retry middleware changes backwards compatible

umrashrf/scrapy,pawelmhm/scrapy,taito/scrapy,Ryezhang/scrapy,pawelmhm/scrapy,rolando-contrib/scrapy,starrify/scrapy,ArturGaspar/scrapy,taito/scrapy,ArturGaspar/scrapy,pawelmhm/scrapy,umrashrf/scrapy,wujuguang/scrapy,pablohoffman/scrapy,Parlin-Galanodel/scrapy,rolando/scrapy,wujuguang/scrapy,wujuguang/scrapy,darkrho/scrapy-scrapy,dangra/scrapy,rolando/scrapy,finfish/scrapy,scrapy/scrapy,pablohoffman/scrapy,rolando-contrib/scrapy,shaform/scrapy,eLRuLL/scrapy,rolando/scrapy,Ryezhang/scrapy,kmike/scrapy,Parlin-Galanodel/scrapy,starrify/scrapy,kmike/scrapy,dangra/scrapy,taito/scrapy,shaform/scrapy,ssteo/scrapy,elacuesta/scrapy,Ryezhang/scrapy,elacuesta/scrapy,eLRuLL/scrapy,finfish/scrapy,ssteo/scrapy,umrashrf/scrapy,ArturGaspar/scrapy,scrapy/scrapy,finfish/scrapy,scrapy/scrapy,darkrho/scrapy-scrapy,pablohoffman/scrapy,Parlin-Galanodel/scrapy,dangra/scrapy,eLRuLL/scrapy,shaform/scrapy,elacuesta/scrapy,rolando-contrib/scrapy,ssteo/scrapy,darkrho/scrapy-scrapy,kmike/scrapy,starrify/scrapy