Cleanup: gcc's -Wcomment warnings

[ideasman42]

Quiets -Wcomment warnings, eg:

toonz/sources/common/psdlib/psd.h:262:2: warning: multi-line comment [-Wcomment]
toonz/sources/image/./psd/../../common/psdlib/psd.h:262:2: warning: multi-line comment [-Wcomment]
toonz/sources/image/psd/../../common/psdlib/psd.h:262:2: warning: multi-line comment [-Wcomment]
toonz/sources/image/psd/tiio_psd.cpp:14:1: warning: multi-line comment [-Wcomment]
toonz/sources/include/toonzqt/gutil.h:50:1: warning: multi-line comment [-Wcomment]
toonz/sources/include/toonzqt/gutil.h:54:1: warning: multi-line comment [-Wcomment]
toonz/sources/toonz/../common/psdlib/psd.h:262:2: warning: multi-line comment [-Wcomment]
toonz/sources/toonzlib/../common/psdlib/psd.h:262:2: warning: multi-line comment [-Wcomment]
toonz/sources/toonzlib/tcenterlineskeletonizer.cpp:1253:1: warning: multi-line comment [-Wcomment]
toonz/sources/toonzlib/tcenterlineskeletonizer.cpp:1355:1: warning: multi-line comment [-Wcomment]
toonz/sources/toonzlib/tframehandle.cpp:25:5: warning: "/*" within comment [-Wcomment]
toonz/sources/toonzqt/../include/toonzqt/gutil.h:50:1: warning: multi-line comment [-Wcomment]
toonz/sources/toonzqt/../include/toonzqt/gutil.h:54:1: warning: multi-line comment [-Wcomment]

[skitaoka]

Jenkins, test this.

[skitaoka]

Jenkins, test this, again.