display-caf: GCC 4.7 Fixes

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common.mk: Disable -Werror for now
libcopybit/copybit_c2d.cpp: signed to unsigned int
libexternal/external.cpp: add DEBUG to ALOGD_IF
libhwcomposer/hwc_mdpcomp.cpp: signed to unsigned int

* Only one that remains is:
narrowing conversion of 'dst->copybit_image_t::w' from 'const uint32_t {aka const unsigned int}'...

Change-Id: I2a1790012cf98987d8f8d2323cdbacde2d4967fd
Signed-off-by: bmc08gt <bmc08gt.teamb00sted@gmail.com>