CRM-13100 Suggested syntax and spelling fixes.

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* CRM-13100: Membership: change text when creating login account
  http://issues.civicrm.org/jira/browse/CRM-13100
Merge pull request #1248 from davecivicrm/CRM-13100

CRM-13100 Suggested syntax and spelling fixes.
Merging my own PR since it's so trivial.