Fix compiler warning: enumerated type mixed with another type
"if(a)" is our style, not "if( a )"
By the use of a the new lib/checksrc.pl script that checks that our basic source style rules are followed.
asyn-ares.c and asyn-thread.c are two separate backends that implement the same (internal) async resolver API for libcurl to use. Backend is specified at build time. The internal resolver API is defined in asyn.h for asynch resolvers.