Splits the progress @echo statements in the Makefile.
Replaces some @echo recipes by @printf.

The echo command does not understand the -n argument on Mac OS X.
This is due to the fact that:

  - Makefile calls /bin/sh to execute a command
  - in Mac OS X, /bin/sh is a link to bash
  - in Mac OS X, bash is compiled with --enable-strict-posix-default

Therefore, the echo command does not have the -n argument.

printf on the other hand is a builtin function that works well on Mac OS X and Linux.
Moves one @printf statement to be more accurate.
Modifies the Makefile to use local npm install **when available**

The change introduced in 5bd8cdca9 was:

  - partial, as not all the command were translated
  - preventing the use of a global npm installation
Allows the user to set different source and destination in Makefile.

A user can use the following command to determine where to copy the resulting css file:

    $ BOOTSTRAP=<my-path> make
Changes some more commands to use the local npm install.
Added retina image support mixin
Added Development > build: "make bootstrap" notes.
Backport v3's readme update on npm install to 2.3
Resolve conflicts
correct version
remove duplicate done text; change label on docs prep step
Merge pull request #6967 from twitter/readme_npm_fix

Update readme npm instructions
remove auto regen
Remove margin between buttons in button groups; use border-radius mixins to avoid reseting border-radii that don't need resetting
le sigh
Fixes #6897: Print styles get own .less file
Fixes #6935: Use standard decimal points for .opacity() mixin
pass true to cycle
rebuild