Revert "Detect busybox logger and change logger cmdline"

This reverts commit 0a056977d736df3adcc16e99a50dd06efbdb7a0e.

That commit is reverted because from now on we will print the
rnapshot's current pid directly in the tag instead of using the
"-i" option of the logger program. Using the "-i" option prints out
the PID of the logger program itself (therefore making it impossible to
correlate log lines and rsnapshot instances when there are multiple ones
running simultaneously).
Print rnspashot's PID when logging to syslog

Print rsnapshot's PID instead of the logger's PID when logging to
syslog. This is much more useful because it allow to relate log
lines to rsnapshot instances when there are multiple concurrent
ones. Previously each line had a different PID, even those
generated by the same instance.

The change is achieved by dropping the "-i" option from the
logger's call and appending the rnapshot's PID to the tag itself.
Ability to wait for other instances to finish

Introduces the ability to wait for other instances to finish their
execution, instead of instantly aborting in this condition. This
feature is implemented by specifying a maximum number of minutes
to wait for the lockfile to be freed.

When set to 0 (default), the previous behavior is unchanged.
Merge remote-tracking branch 'remotes/origin/syslog-pid'

Conflicts:
	ChangeLog