linux_Makefile: gprof

patience: reduce sections by swallowing identical lines before LCS

move struct range defs to diff_main.h (prep for upcoming patch)

lib/linux_Makefile: -O3

debug: dump at most 42 lines

debug: dont dump too large myers graphs

dont escape tabs in text output

myers: permit ~4Mb of state

switch default to unidiff

initial commit