Add missing platform constants

[th-otto]

Q	A
Bug fix?	yes
New feature?	no

This adds missing OS_* constants, using the same names that ZipArchive uses. Note that there might be some discrepancy (haven't checked yet whether it is a fault of php's ZipArchive or the underlying ziplib), but InfoZIP uses some different constants in a few places:

#define FS_TOPS20         10
#define FS_NTFS           11			/* filesystem used by Windows NT */
#define FS_QDOS           12

whereas ZipArchive uses

ZipArchive::OPSYS_WINDOWS_NTFS = 10
ZipArchive::OPSYS_MVS = 11
ZipArchive::OPSYS_VSE = 12