Don't require an IDE preferences file, fallback to default sketchbook.

It should be possible to use the Makefile without ever running the
Arduino or chipKIT IDE. This change only looks for the preferences file
if the sketchbook path is not defined, and even then, will use the
default skethbook path if the preferences file is unavailable.

arduino-mk/Arduino.mk

@@ -285,7 +285,9 @@ endif
 # Arduino Sketchbook folder
 #
 
-ifndef ARDUINO_PREFERENCES_PATH
+
+ifndef ARDUINO_SKETCHBOOK
+    ifndef ARDUINO_PREFERENCES_PATH
 
         AUTO_ARDUINO_PREFERENCES := $(firstword \
             $(call dir_if_exists,$(HOME)/.arduino/preferences.txt) \
@@ -293,22 +295,17 @@ ifndef ARDUINO_PREFERENCES_PATH
         ifdef AUTO_ARDUINO_PREFERENCES
            ARDUINO_PREFERENCES_PATH = $(AUTO_ARDUINO_PREFERENCES)
            $(call show_config_variable,ARDUINO_PREFERENCES_PATH,[AUTODETECTED])
+        endif
+
     else
-        echo $(error "ARDUINO_PREFERENCES is not defined")
-    endif
-
-else
         $(call show_config_variable,ARDUINO_PREFERENCES_PATH,[USER])
-endif
-
-ifndef ARDUINO_SKETCHBOOK
-    ifeq ($(ARDUINO_PREFERENCES_PATH),)
-        echo $(error No ARDUINO_PREFERENCES_PATH detected, cannot autodetect ARDUINO_SKETCHBOOK)
     endif
 
+    ifneq ($(ARDUINO_PREFERENCES_PATH),)
         ARDUINO_SKETCHBOOK = $(shell grep --max-count=1 --regexp="sketchbook.path=" \
                                           $(ARDUINO_PREFERENCES_PATH) | \
                                      sed -e 's/sketchbook.path=//' )
+    endif
 
     ifneq ($(ARDUINO_SKETCHBOOK),)
         $(call show_config_variable,ARDUINO_SKETCHBOOK,[AUTODETECTED],(from arduino preferences file))

arduino-mk/chipKIT.mk

@@ -62,8 +62,6 @@ ifndef MPIDE_PREFERENCES_PATH
     ifdef AUTO_MPIDE_PREFERENCES_PATH
        MPIDE_PREFERENCES_PATH = $(AUTO_MPIDE_PREFERENCES_PATH)
        $(call show_config_variable,MPIDE_PREFERENCES_PATH,[autodetected])
-    else
-        echo $(error "MPIDE_PREFERENCES_PATH is not defined")
     endif
 endif