Use reenterant versions of time functions!

Replace use of gmtime, localtime and asctime in sconex/Time and sconex/Date
with the equivalent _r versions. This was causing the incorrect time to be
returned infrequently and randomly, probably manifesting in a range of bugs.
One in particular, which resulting in me finding this issue, was that
frequently used HTTP sessions would randomly expire after a while.
Add http as a module dependency for rss

The rss module now depends on http since it uses http::Client to download
feeds. Add this dependency to the module configuration file so http is loaded
before rss.
Update debian changelog for 0.9.8ppa6 build
Use reenterant version of readdir in sconex/FileDir

Use readdir_r instead of readdir since this may cause problems when calling
from multiple threads.
Use reenterant versions of passwd functions in sconex/User

Replace use of getpwnam and getpwuid with reenterant versions since this may
cause problems when calling from multiple threads.
Usage of these in sconex/Process is OK since these are called in the single
threaded root proxy process.
Use reenterant versions of resolver functions in ip and ip6

Replace use of gethostbyname, gethostbyaddr, getservbyname and getservbyport
with the equivalent reenterant versions, since these may cause problems when
calling from multiple threads.
Update debian changelog for 0.9.8ppa7