TracTimeline navigation fixes:  - use the request's timezone for defining 'today' (#4758)  - keep the current ''daysback'' parameter in the navigation links  - fix the check for the ''Next period'' link (#4757)
TracTimeline navigation fixes:
 - use the request's timezone for defining 'today' (#4758)
 - keep the current ''daysback'' parameter in the navigation links
 - fix the check for the ''Next period'' link (#4757)

Thanks to Sergei Haller for reporting those issues and providing a patch for #4757.

git-svn-id: f68c6b3b1dcd5d00a2560c384475aaef3bc99487@4765 af82e41b-90c4-0310-8c96-b1721e28e2e2

dokipen/trac,dokipen/trac,exocad/exotrac,exocad/exotrac,dafrito/trac-mirror,dafrito/trac-mirror,moreati/trac-gitsvn,dafrito/trac-mirror,exocad/exotrac,dokipen/trac,moreati/trac-gitsvn,moreati/trac-gitsvn,exocad/exotrac,moreati/trac-gitsvn,dafrito/trac-mirror