update of a long row can fail with ERROR nospc: nospc.U exception.

An update of a row fails with a nospc.U exception. If there is space on the disk then an update should never fail for a space
issue. The code is meant to always reserve enough space on a page such that if an expanding update happens that does not
fit, it should in the worst case change the row to an overflow row pointer and put the rest in a linked overflow chain.

The following set of circumstances will cause this bug (not sure which are exactly needed - just what i did to
cause the repro), I will be attaching a test case:
The row being updated has the following characteristics:
o located on 4k page
o 2 colum row with 2nd column a blob column
o the row is a long row with first piece having 1st column on main page, and the 2nd piece having just blob column on overflow page.
o before the update there is 0 free space on the overflow page.
o the update causes the blob column to expand past 4k

Caused by: java.sql.SQLException: nospc.U
at org.apache.derby.impl.jdbc.SQLExceptionFactory.getSQLException(SQLExceptionFactory.java:45)
at org.apache.derby.impl.jdbc.SQLExceptionFactory40.wrapArgsForTransportAcrossDRDA(SQLExceptionFactory40.java:119)
at org.apache.derby.impl.jdbc.SQLExceptionFactory40.getSQLException(SQLExceptionFactory40.java:70)
... 39 more
Caused by: ERROR nospc: nospc.U
at org.apache.derby.impl.store.raw.data.StoredPage.logRow(StoredPage.java:4155)
at org.apache.derby.impl.store.raw.data.UpdateOperation.writeOptionalDataToBuffer(UpdateOperation.java:255)
at org.apache.derby.impl.store.raw.data.UpdateOperation.<init>(UpdateOperation.java:106)
at org.apache.derby.impl.store.raw.data.LoggableActions.actionUpdate(LoggableActions.java:80)
at org.apache.derby.impl.store.raw.data.StoredPage.doUpdateAtSlot(StoredPage.java:8625)
at org.apache.derby.impl.store.raw.data.BasePage.updateAtSlot(BasePage.java:1062)
at org.apache.derby.impl.store.access.conglomerate.GenericConglomerateController.replace(GenericConglomerateController.java:486)
at org.apache.derby.impl.sql.execute.RowChangerImpl.updateRow(RowChangerImpl.java:523)
at org.apache.derby.impl.sql.execute.UpdateResultSet.collectAffectedRows(UpdateResultSet.java:569)
at org.apache.derby.impl.sql.execute.UpdateResultSet.open(UpdateResultSet.java:264)
at org.apache.derby.impl.sql.GenericPreparedStatement.executeStmt(GenericPreparedStatement.java:436)
at org.apache.derby.impl.sql.GenericPreparedStatement.execute(GenericPreparedStatement.java:317)
at org.apache.derby.impl.jdbc.EmbedStatement.executeStatement(EmbedStatement.java:1241)
... 33 more