hgmerge: fix diff+patch detection; cleanups
Details:
- actually show help message when no tools are found
- whitespace cleanup (stupid emacs)
- quote more variables
- simplify merge/diff3 error handling
header = header-raw.tmpl
footer = ""
changeset = changeset-raw.tmpl
difflineplus = "#line#"
difflineminus = "#line#"
difflineat = "#line#"
diffline = "#line#"
changesetparent = "# parent: #node#"
changesetchild = "# child: #node#"
filenodelink = ""
filerevision = filerevision-raw.tmpl
fileline = "#line#"
diffblock = "#lines#"
filediff = filediff-raw.tmpl
fileannotate = fileannotate-raw.tmpl
annotateline = "#author#@#rev#: #line#"