curl tool: fix a bunch of double free's uncovered 2011-09-15

Re-enabling MemoryTracking capability on 'src' subdirectory files and torture
tests have uncovered many issues which were going unnoticed in curl tool. So
here we go fixing some of them. Others still remain and should be addressed
ASAP, given that curl tool is used in our test harness also for test server
start verification purposes. There are even non-socket file descriptor leaks.