Tweak the membership start and end dates calculation for fixed membership period.

It looks like membership start and end dates calculation is not doing well for some scenarios with fixed membership period. Some basic rules:

1. Membership start date ALWAYS is equal to current fixed period's beginning date (membership start date should NEVER be set to a future date).
2. If member's join date >= rollover date AND < fixed-period start day, then member end date = end of NEXT fixed membership period.

Consider Following scenarios for fixed membership period :

Scenario A :
Start = 1 April
Duration = 1 year
Rollover = 1 March

Membership sign up = 25th March 2011

Expected membership dates should be :
Join = 25March March 2011
Start = 1 April 2010 (1st day of current fixed membership period)
End = 31 March 2012 (end of NEXT fixed membership period)

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Scenario B :
Start = 1 Sep
Duration = 1 year
Rollover = 30 June

Membership sign up = 15 January 2011

Expected membership dates should be :
Join = 15 Jan 2011
Start = 1 Sep 2010 (1st day of current fixed membership period)
End = 31 Aug 2011 (end of current fixed membership period, since we are before the rollover day of 30 June)

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Scenario C :
Start = 1 June
Duration = 1 year
Rollover = 31 Aug

Membership sign up = 5 January 2011

Expected membership dates should be :
Join = 5 Jan 2011
Start = 1 June 2010 (1st day of current fixed membership period)
End = 31 May 2012 (end of NEXT fixed membership period, since 5 Jan is afterthe rollover day of 31 Aug)

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Scenario D :
Start = 1 April
Duration = 1 year
Rollover = 1 Jan

Membership sign up = 5th April 2011

Expected membership dates should be :
Join = 5 April 2011
Start = 1 April 2011 (1st day of current fixed membership period)
End = 31 March 2012 (end of current fixed membership period, since we are before the rollover day of 1 Jan )

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Related forum threads is here : http://forum.civicrm.org/index.php/topic,18074.0/topicseen.html

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There are few issues in the recent past :
http://issues.civicrm.org/jira/browse/CRM-7392
http://issues.civicrm.org/jira/browse/CRM-6079

Also It would be great to have web test for membership calculation, once we fixed this issue.