BUG: Fix ITK prepare-commit-msg hook for non-GNU sed
BUG: Fix ITK prepare-commit-msg hook for non-GNU sed

An expression of the form \(a\|b\) is a GNU sed extension.  Re-implement
insertion of the commit message prefix instructions to use portable sed
capabilities.

Conflicts:

	Utilities/Hooks/prepare-commit-msg

SimpleITK/SimpleITK,hendradarwin/SimpleITK,InsightSoftwareConsortium/SimpleITK,SimpleITK/SimpleITK,kaspermarstal/SimpleElastix,SimpleITK/SimpleITK,kaspermarstal/SimpleElastix,SimpleITK/SimpleITK,InsightSoftwareConsortium/SimpleITK,richardbeare/SimpleITK,blowekamp/SimpleITK,SimpleITK/SimpleITK,richardbeare/SimpleITK,SimpleITK/SimpleITK,blowekamp/SimpleITK,blowekamp/SimpleITK,blowekamp/SimpleITK,InsightSoftwareConsortium/SimpleITK,kaspermarstal/SimpleElastix,hendradarwin/SimpleITK,richardbeare/SimpleITK,hendradarwin/SimpleITK,InsightSoftwareConsortium/SimpleITK,blowekamp/SimpleITK,SimpleITK/SimpleITK,InsightSoftwareConsortium/SimpleITK,hendradarwin/SimpleITK,kaspermarstal/SimpleElastix,blowekamp/SimpleITK,hendradarwin/SimpleITK,hendradarwin/SimpleITK,kaspermarstal/SimpleElastix,blowekamp/SimpleITK,hendradarwin/SimpleITK,InsightSoftwareConsortium/SimpleITK,richardbeare/SimpleITK,richardbeare/SimpleITK,kaspermarstal/SimpleElastix,richardbeare/SimpleITK,InsightSoftwareConsortium/SimpleITK,richardbeare/SimpleITK,kaspermarstal/SimpleElastix,richardbeare/SimpleITK,InsightSoftwareConsortium/SimpleITK,hendradarwin/SimpleITK,SimpleITK/SimpleITK,blowekamp/SimpleITK