logcat: -f flag to continue

On startup, check the current logging content, then grab logs from
that time forward rather than restarting from the beginning. Add
support for reading tail time down to the nano-second.

Bonus, permits us to create a logcatd logpersist daemon

Bug: 19608716
Change-Id: Iaab58de4c02b7f97c69de12cf954fedc2163059e
diff --git a/logcat/Android.mk b/logcat/Android.mk
index f46a4de..fd54915 100644
--- a/logcat/Android.mk
+++ b/logcat/Android.mk
@@ -5,7 +5,7 @@
 
 LOCAL_SRC_FILES:= logcat.cpp event.logtags
 
-LOCAL_SHARED_LIBRARIES := liblog
+LOCAL_SHARED_LIBRARIES := liblog libbase
 
 LOCAL_MODULE := logcat