allow user to escape the escape_char as well

msf  exploit(psexec) > set SMBPass foo;set SMUser bar
SMBPass => foo
SMUser => bar
msf  exploit(psexec) > set SMBPass foo\;bar;set SMUser bar
SMBPass => foo;bar
SMUser => bar
msf  exploit(psexec) > set SMBPass foo\\;bar;set SMUser bar
SMBPass => foo;bar
SMUser => bar
msf  exploit(psexec) > set SMBPass foo\\\;bar;set SMUser bar
msf  exploit(psexec) > set SMBPass foo\\bar;set SMBUser bar
SMBPass => foo\bar
SMBUser => bar
msf  exploit(psexec) > set SMBPass fo\\o\\bar;set SMBUser bar
SMBPass => fo\o\bar
SMBUser => bar