TS-1086: Avoid returning 304 to an unconditional request.
Diagnosis and patch by Mohamad Khateeb.
TS-2191 we should not simply reschdule the http_sm if the sm_list`s mutex
is not acquired, because the client_vc`s timeout events maybe triggered.
The race may lead http_sm received a event after it is deleted.
Sub task (TS-2192)
TS-2188 healthcheck plugin doesn't parse config files properly

This is part of the fixes to the healthcheck plugins, such that
we don't segfault. This part of the fix actually makes sure we
properly parse the configuration file as was expected.
TS-2188 Never consider a simple / path as a healthcheck

This is an optimization, and a safety net, such that a simple
/ path can never be considered for a healthcheck.
Updated text / format.
TS-2176: do not reset value of api_skip_cache_lookup when reading it

When is_request_cache_lookupable reads the value of api_skip_cache_lookup
it also resets the value to false.  Since the function is called
from HandleRequest, the flag set by the API call will be ignored
by DecideCacheLookup.
Use proper sentences in CHANGES
TS-2195: Deprecate experimental TSHttpTxnCacheLookupSkip API

TSHttpTxnCacheLookupSkip() is in experimental, but can be implemented
by stable API; TSHttpTxnConfigIntSet(txn, TS_CONFIG_HTTP_CACHE_HTTP, 0).
remove Makefile-pl on make distclean
TS-2195: reimplement TSHttpTxnCacheLookupSkip in terms of TSHttpTxnConfigIntSet

Replace the guts of TSHttpTxnCacheLookupSkip with TSHttpTxnConfigIntSet.
This is a compatible change that makes it easy to remove
TSHttpTxnCacheLookupSkip in the 5.x branch.
initialize HttpTunnelProducer::last_state to a default value
Remove <tab>s from indentation
TS-2185: support to control ClusterCom::sendSharedData frequency
TS-1637: Fix nodes as idle/dead if we have not heard from them in awhile
TS-2207: CentOS5 out of tree perl module build fails

The older version of automake on CentOS5 doesn't supply the $(builddir)
variable, possibly because it's implicitly the current working
directory. It also doesn't supply various $abs_ variables that later
versions do. Rewrite the copy using more fundamental automake
variables.
TS-2206 The trafficserver RC script does not use absolute path to
traffic_line binary.
TS-2207: stop using $(builddir) in automake

Older automake (< 1.9?) doesn't emit $(builddir), but it's always
"." anyway, so let's use that instead.
Fixed indentation
ci: all centos versions have redhat-lsb
TS-2187: use nonblock eventfd in EventNotify

1) Use nonblock eventfd, so that we can tolerate write() failed with
   errno EAGANIN – which is acceptable as the signal receiver will be
   notified eventually in this case.

2) After using nonblock eventfd, read() will not block in wait(). So
   I use epoll_wait() to implement block behavior, just like timedwait().

3) nonblock eventfd can fix a potential problem: if receiver didn't
   read() data immediately, senders might block in write().

Signed-off-by: Yunkai Zhang <qiushu.zyk@taobao.com>