`port outdated` seems to fail on macOS Sierra, 10.12.2

[ballapete (Peter "Pete" Dyballa)]

ort outdated
The following installed ports are outdated:
cmake                          3.7.1_0 < 3.7.2_0         
can't use non-numeric string as operand of "-"
    while executing
"expr {$installed_revision - $latest_revision}"
    (procedure "action_outdated" line 84)
    invoked from within
"$action_proc $action $portlist [array get global_options]"
    (procedure "process_cmd" line 103)
    invoked from within
"process_cmd $remaining_args"
    invoked from within
"if { [llength $remaining_args] > 0 } {

    # If there are remaining arguments, process those as a command
    set exit_status [process_cmd $remaining..."
    (file "/opt/local/bin/port" line 5286)}}}

and similarly:

{{{
sudo port upgrade outdated
Password:
can't use non-numeric string as operand of "-"
    while executing
"expr {$installed_revision - $latest_revision}"
    (procedure "get_outdated_ports" line 65)
    invoked from within
"get_${name}_ports"
    ("^outdated(@.*)?$" arm line 8)
    invoked from within
"switch -regex -- $token {
        ^\\)$               -
        ^\;                 -
        ^_EOF_$             { # End of expression/cmd/file
     ..."
    (procedure "element" line 12)
    invoked from within
"element reslist"
    (procedure "unaryExpr" line 17)
    invoked from within
"unaryExpr reslist"
    (procedure "andExpr" line 4)
    invoked from within
"andExpr reslist"
    (procedure "orExpr" line 4)
    invoked from within
"orExpr blist"
    (procedure "seqExpr" line 16)
    invoked from within
"seqExpr reslist"
    (procedure "portExpr" line 3)
    invoked from within
"portExpr portlist"
    (procedure "process_cmd" line 93)
    invoked from within
"process_cmd $remaining_args"
    invoked from within
"if { [llength $remaining_args] > 0 } {

    # If there are remaining arguments, process those as a command
    set exit_status [process_cmd $remaining..."
    (file "/opt/local/bin/port" line 5286)
}}}