minor errors in docs/users_guide/6.12.1-notes.xml

• listitem is misspelled a total of 4 times as listierm (two open tags, two close tags).
• The -fwarn-unused-do-bind flag is documented in two items. Probably the second item should be removed. It would be nice to include a link to the relevant part of Section 4.7 in the first item.

Trac metadata

Trac field	Value
Version	6.11
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Documentation
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