test-bisect: test handling of invalid commands without relying on sh

diffhelpers: fix variable declaration for MSVC (not C99)

dirstate: improve docstring formatting Triple-quoted strings are easier to spot than single-quoted strings.

test-help: improve test coverage Adds a test for displaying a help topic. Extends test coverage of commands.help_ by 5 lines.

test-help: improve test coverage Adds a test for displaying a command list with a command with no help text. Extends test coverage of commands.help_ by 1 line.

test-help: improve test coverage Adds a test that extension commands are omitted from the default command list. Extends test coverage of commands.help_ by 1 line.

test-help: improve test coverage Adds a test for commands without help text. Extends test coverage of commands.help_ by 1 line.

test-help: improve test coverage Adds a test for help on a command with no options. Extends test coverage of commands.help_ by 2 lines.

test-help: improve test coverage Adds a test for handling ambiguous command help Extends test coverage of commands.help_ by 4 lines.

merge with stable

monoblue: fix title for branches page

Merge with crew-stable

patch: better handling of sequence of offset patch hunks (issue1941) The built-in patch implementation applied the hunks to the wrong lines of the file if the file in the repo has been modified to skew the patch line numbers and the file contains repetitive sequences of lines.

Makefile: added instructions on how to override PREFIX