CRM-13231 - Fix warning in postUpgradeMessage for missing cost of sales linkage. Add link to wiki page for instructions on fixing.

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* CRM-13231: Incremental upgrade 4.3.4 fails if no COGS and EXP default account set
  http://issues.civicrm.org/jira/browse/CRM-13231
Merge pull request #1665 from davecivicrm/CRM-13231

CRM-13231 - Fix warning in postUpgradeMessage for missing cost of sales ...