Set default value for upload.verify

Arduino IDE 1.6.9 and newer allow the -V option to be added to the
AVRDUDE command if File > Preferences > Verify code after upload is
unchecked. In previous versions of the IDE this option had no effect,
going back for some time. As with many changes made to the IDE, this
broke backwards compatibility, though in this case there was delay.

Arduino AVR Boards 1.6.11 added the {upload.verify} property to the
tools.avrdude.upload recipe to support the File > Preferences > Verify
code after upload setting. In Arduino IDE versions 1.6.8 and previous
this property is set to true or false depending on the preferences
setting which causes Upload with Arduino IDE 1.6.8 to generate AVRDUDE
commands like:

avrdude
-CE:\Stuff\misc\electronics\arduino\hardware\MiniCore\avr/avrdude.conf
-v true -patmega328p -carduino -PCOM21 -b115200 -D

-Uflash:w:C:\Users\per\AppData\Local\Temp\buildb7baad927be9bdd89a5f10c3d4ed06ef.tmp/sketch_sep28a.ino.hex:i

AVRDUDE 6.0.1 is able to ignore the spurious true/false item in the
command and successfully upload but when used with AVRDUDE 6.3.0 this
causes upload to fail:

avrdude: no programmer has been specified on the command line or the
config file
Specify a programmer using the -c option and try again

This issue will occur if MiniCore is used with with Arduino IDE 1.6.8
and previous and Arduino AVR Boards 1.6.12 or 1.6.14.

Setting a default empty value for the upload.verify property in
platform.txt causes Arduino IDE 1.6.8 and older to generate an AVRDUDE
command identical to that generated with Arduino AVR Boards 1.6.10 or
older(meaning that, as previously, the preferences setting has no
effect):

avrdude
-CE:\Stuff\misc\electronics\arduino\hardware\MiniCore\avr/avrdude.conf
-v -patmega328p -carduino -PCOM21 -b115200 -D

-Uflash:w:C:\Users\per\AppData\Local\Temp\buildb7baad927be9bdd89a5f10c3d4ed06ef.tmp/sketch_sep28a.ino.hex:i

Arduino IDE 1.6.9 and newer overrides the default value of
upload.verify, therefore this change has no effect on the AVRDUDE
command generated and verification is controlled by the preferences
setting as usual.

Author: per1234

avr/platform.txt

@@ -97,6 +97,8 @@ tools.avrdude.config.path={runtime.platform.path}/avrdude.conf
 
 tools.avrdude.upload.params.verbose=-v
 tools.avrdude.upload.params.quiet=-q -q
+# tools.avrdude.upload.verify is needed for backwards compatibility with AVRDUDE 6.3.0 and IDE 1.6.8 or older, IDE 1.6.9 or newer overrides this value
+tools.avrdude.upload.verify=
 tools.avrdude.upload.params.noverify=-V
 tools.avrdude.upload.pattern="{cmd.path}" "-C{config.path}" {upload.verbose} {upload.verify} -p{build.mcu} -c{upload.protocol} -P{serial.port} -b{upload.speed} -D "-Uflash:w:{build.path}/{build.project_name}.hex:i"