connect: rename tortoiseplink and putty variables

connect: rename tortoiseplink and putty variables

One of these two may have originally been named after "what exact
SSH implementation do we have?" so that we can tweak the command
line options for that exact implementation.  But "putty=1" no longer
means "We are using the plink SSH implementation that comes with
PuTTY" these days.  It is set when we guess that either PuTTY plink
or Tortoiseplink is in use.

Rename them after what effect is desired.  The current 'putty'
option is about using "-P <port>" when OpenSSH would use "-p <port>",
so rename it to 'port_option' whose value is either 'p' or 'P".  The
other one is about passing an extra command line option "-batch",
so rename it to 'needs_batch'.

[jes: wrapped overly-long line]

Signed-off-by: Junio C Hamano <redacted>
Signed-off-by: Johannes Schindelin <redacted>
Signed-off-by: Junio C Hamano <redacted>