Fix warnings produced by texinfo 7.0.2
When building cmu-user with texinfo 7.0.2, there are warnings now:
TEXINPUTS=..:$TEXINPUTS makeinfo --info cmu-user.texi
debugger.texi:1240: warning: @ref node name should not contain `:'
debugger.texi:1247: warning: @ref node name should not contain `:'
debugger.texi:1247: warning: @ref node name should not contain `:'
debugger.texi:1247: warning: @ref node name should not contain `:'
compiler.texi:237: warning: @xref cross-reference name should not contain `:' (possibly involving @keyref)
compiler.texi:1266: warning: @xref cross-reference name should not contain `:' (possibly involving @keyref)
compiler.texi:1266: warning: `.' or `,' must follow @xref (possibly involving @keyref)
compiler-hint.texi:140: warning: @xref cross-reference name should not contain `:' (possibly involving @keyref)
We should fix these warnings. And check the other docs to see if there are warnings there too.