Applied bug fix from trunk r1639848.
Applied patch from jira issue - OFBIZ-5630 - service updateFxConversion doesn't set thruDate properly.
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When updating an existing foreign currency exchange rate in accounting the service creates a new exchange rate and sets the thruDate of the old rate.
But in stead of taking the fromDate of the new exchange rate as a starting point for the thruDate of the expired exchange rate it uses nowTimeStamp.
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Thanks Pierre for reporting the issue. Thanks Pranay for providing the fix.

git-svn-id: https://svn.apache.org/repos/asf/ofbiz/branches/release12.04@1639852 13f79535-47bb-0310-9956-ffa450edef68